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04_12_87/T\OSB07
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.
| Tape/disk: | Home » CEEFAX disks » telesoftware3.adl |
| Filename: | 04_12_87/T\OSB07 |
| Read OK: | ✔ |
| File size: | 318C bytes |
| Load address: | 0000 |
| Exec address: | 0000 |
File contents
OSBITS - An Exploration of the BBC Micro at Machine Level
By Programmer
...........................................................
Part 7: Operating System Calls (II) - I/0
In this second look at operating system routines I'll deal
with those relating to input and output. It's one of the
beauties of the BBC Micro OS that the routines for input and
output (I/O) are independent of the source or destination of
that I/O. The selection of source and destination (known as
the input and output stream) are the province of some of the
OSBYTE calls.
To summarise the I/O routines first:
Input is handled by OSRDCH which stands for OS Read
Character
Output is handled by OSWRCH which stands for OS Write
Character together with the related calls OSASCI and OSNEWL
Selection of source is by using OSBYTE 2
Selection of destination is by using OSBYTE 3
To recap, the OS routines are in fact subroutines entered at
known addresses in the OS ROM. To use them the necessary
values for the registers are set and then you JSR to the
routine and it will RTS back to you when its work is done.
OSRDCH starts at address &FFE0 and when called it works
rather like the GET function in BBC BASIC. It will wait for
the next character to enter the input buffer for whichever
stream is selected and put it, or rather its ASCII value,
into the accumulator.
An error can occur while OSRDCH is operating. The most
common is an ESCAPE in which case A will contain 27 and the
carry flag will be set, as it is for any error. An ESCAPE
must be acknowledged by calling OSBYTE 126.
OSWRCH starts at address &FFEE and takes the ASCII value in
the accumulator and sends it to the current output stream.
Note that if certain control codes are sent to the VDU
drivers, i.e. the screen, then some bytes following will be
interpreted as parameters for VDU commands such as PLOT and
TAB equivalents.
[This is not the case when sending to, say, a printer only,
when all bytes are passed on. There is a difference here
between the effect of defining printer as the only output
stream using OSBYTE 3 and prefixing a string of bytes with a
2 (as in VDU2) to select the printer. In the latter case
the bytes associated with control codes are not sent.]
There are two other routines related to OSWRCH. OSASCI,
which starts at &FFE3, behaves exactly as OSWRCH except when
the byte passed is 13 (&0D) which is a carriage return. In
this case a line feed (10 or &0A) is sent followed by a
carriage return. In other words a new line is selected.
The code to do this is contained in OSNEWL at &FFE7 which,
when called, will send a line feed followed by a carriage
return.
[As another aside, the choice of LF then CR is curious as
the 'standard' dating from the days of mechanical teletypes
is for a CR then an LF. This was so that during the
carriage flyback a line feed would occur rather than a
printable character. The appearance of a printable
character at this time would probably result in it being
printed during the flyback! If you ever send a telex from
your micro make sure you perform a new line as CR+LF for
that reason.]
The input and output streams are these:
For input you have the keyboard and the RS423. For output
you have the screen (VDU), printer, RS423 and a spooled
file. Note that the printer could operate through the
RS423.
Input selection is using OSBYTE 2 (*FX2) and you have three
choices. The accumulator, obviously, contains 2.
If X contains 0 (default) then the keyboard will be selected
and the RS423 will be disabled (this means no carrier would
be sent by a modem for example).
If X contains 1 then the RS423 is both enabled and selected
as input.
If X contains 2 then the RS423 is enabled but input is from
the keyboard.
When OSBYTE 2 has been called the X register will contain a
0 if the previous input was from the keyboard and a 1 if it
came from the RS423.
Output selection is by using OSBYTE 3 and Y should contain
0. The selection or not of a particular output is related
to the bits of X like this.
If bit 0 is set then the RS423 driver is on
If bit 1 is set then the VDU driver is off
If bit 2 is set then the printer driver is off
If bit 3 is set then the printer is selected without VDU 2
If bit 4 is set then the spooled output is disabled
If bit 6 is set then the printer is disabled (except for
characters preceded by VDU 1)
Bits 5 and 7 are not used.
The default is X=0 which means the RS423 is disabled, the
VDU is selected and the printer driver is on if it is
selected by VDU 2. You can also spool to a file.
To send to a printer only then X should be set to 10. All
characters will then go to the printer without being checked
by the VDU drivers for control codes etc. Note that in the
case of a spooled file you only enable the facility with
OSBYTE 3 and do not actually generate the file itself. That
has to be done separately such as by *SPOOL filename.
After using OSBYTE 3 the X register will contain a byte
holding the previous output stream configuration. This
information would be useful if you wanted to change the
output stream temporarily, do something, and then return to
its previous configuration.
You use OSBYTE 5 to select the printer destination you want
with a choice of a sink (i.e. characters just vanish, useful
for debugging), parallel, RS423, network and user routines.
I won't go into detail here, you should refer to an advanced
reference or user guide for information about all these
calls.
I've already said that sending to the VDU drivers with
OSWRCH (and OSASCI) will sometimes carry out plots and the
like. In fact you can think of these two as being the same:
LDA #19:JSR oswrch:LDA #2:JSR oswrch:LDA #4:JSR oswrch:
LDA #0:JSR oswrch:JSR oswrch:JSR oswrch
and
VDU 19,2,4,0,0,0
and they both set logical colour 2 to actual colour 4.
Apart from the restriction that you have to work a byte at a
time the use of OSWRCH in this way is exactly like BASIC's
VDU codes for graphics and user defined characters and so on.
The bytes to be sent down OSWRCH could be sent from a list,
and there is an example of this in the program in the first
module B/osb01 which prints out a message in this way.
In a later module I will deal with modifying these OS
routines for your own nefarious purposes by making use of
the vectors.
And so to this module's program. It is, I hope, reasonably
self documenting and uses OSWRCH in a number of ways to
print out a string proportionally spaced.
The string to be printed is passed to the routine from BASIC
using CALL with parameters. I've used this method to make
it easy for you to experiment using the routine in your own
programs. There is an important point to be made using CALL
for machine code however, and that is the use of zero page
for post-indexed indirect addressing. Now I know that's a
bit of a mouthful but this is what it looks like.
LDA (zp), Y
In this case A is loaded with the value stored Y bytes above
the address stored in zp and zp+1. zp is in zero page and
you have to use the Y register for the index. If you
remember that in 6502 assembler (memory) means the address
stored in locations memory and memory+1 you should not go
far wrong.
[There is another, somewhat more esoteric, addressing mode
called pre-indexed indirect addressing which uses X as an
index and is written
LDA (zp, X)
In this case A is loaded with the value stored at the
address stored in zp+X and zp+X+1.]
Post (and pre) indexed addressing is also used with
mnemonics other than LDA. If you design and write a
sideways ROM which needs some private workspace, this is the
sort of ROM that raises the value of PAGE, then the OS will
allocate that workspace for you. To actually use this
memory is not straightforward because you have to find out
where it is from the OS when the ROM is initialised. So you
put the workspace address into a couple of addresses in zero
page you use post-indexed indirect addressing to access it.
When you use CALL from BASIC with a set of parameters
attached BASIC allocates a block of memory starting at &600
where these parameters are stored. If, however, one of
these parameters is a string then the &600 block only
contains a pointer to the start of a string information
block. If you transfer this pointer into zero page you can
then use post-indexed indirect addressing to look through
the block, which is what B/osb07 does.
Let's start at the beginning. B/osb07 only sets up the
routine which will print out a string proportionally spaced.
To use it you must be in Mode 1 or Mode 4 and define a
string variable to be your required string, let's call it
M$. The graphics cursor must be positioned where you want
the printing to start by using MOVE.
Then, since code% is the address of the routine, you
CALL code%, M$
When you have run the assembler press f2 and a little
sentence will be printed in Mode 4. Without shadow memory
or a second processor you will not be able to get into Mode
1 with the assembler source in memory.
The variable block% is defined as being &600, which is where
the CALL parameter block lives. At block% itself is stored
the number of parameters; we want a single one and if there
are more we exit because there has been a mistake. I could
have made the routine print out a message saying "Too Many
Parameters for Proportional Spacing" or even generated an
error, but for the moment I'll just exit. Error trapping
will appear in a later module.
At block%+3 is a byte which tells us what kind of parameter
we have. If it is 129 then we have a string. (Full details
of CALL with parameters is in the User Guide.)
Once satisfied that we have a single string parameter
available the program takes the address stored at block%+1
and block%+2 and copies it to a pair of zero page addresses.
I chose &8A and &8B for this and zero_page% is defined as
&8A early in the code.
Initially these will contain the address of a string
information block. The first two bytes of this block hold
the address of the string itself and the third holds its
length. If you can figure out this incredibly convoluted
routine then you're not doing badly.
The string length is stored away and then the start address
is moved into our two zero page addresses with the help of a
little bouncing to and from the stack.
The next section stores the graphics cursor position, using
OSWORD &D, in a block at os_block%. The X co-ordinates will
be held from 4 bytes above os_block% itself and I have
arranged for this to be address gpos. See lines 1930 and
1940. The reason for storing the old X position is so that
if a carriage return is included in the string a new line
will start directly under the start of the last one.
Next the routine filters out any characters below 32 and
above 127 since they are not printable (excepting a carriage
return). On a new line the graphics cursor is moved down by
8 graphics units (i.e. the numbers used by a MOVE or PLOT)
to space the lines out a little more (like Mode 6 would
rather than Mode 4) and you will see in lines 840 to 950
that the assembler equivalent of a relative MOVE has been
carried out using OSWRCH.
The proportional spacing works by looking up in a table how
many 'spare' pixels there are in front and behind a
character. There will be spare pixels because the OS
defines all characters in an 8x8 block. We can ignore the 8
pixels upwards. Here are two characters of different
widths:
** ** *** The W is 7 pixels
** * ** ** wide and the l is
** * ** ** only 4 wide. Both
******* ** are only 7 deep as
*** *** ** neither has a
** ** **** descender.
So you can see that some characters occupy less of the 8
pixels across than others.
The idea is for there to be a single pixel between adjacent
characters and this is assumed to be the first of the 8
pixels across the character to the right. This information
could be calculated by using OSWORD &A to read the OS
definitions but a table is faster to use if slower to work
out in the first place. You can see the table from line
1660.
So the routine moves the next character across to the left
before printing it such that only one pixel will separate it
from the previous one. In MODE 1 and MODE 4 one pixel is
four graphics units wide, hence the 4 in line 1510.
In the next module I shall move back to basics briefly with
logical operators AND ORA EOR BIT which will explain what
line 1260 is all about (if you haven't already figured it
out).
00000000 4f 53 42 49 54 53 20 2d 20 41 6e 20 45 78 70 6c |OSBITS - An Expl| 00000010 6f 72 61 74 69 6f 6e 20 6f 66 20 74 68 65 20 42 |oration of the B| 00000020 42 43 20 4d 69 63 72 6f 20 61 74 20 4d 61 63 68 |BC Micro at Mach| 00000030 69 6e 65 20 4c 65 76 65 6c 0d 0d 42 79 20 50 72 |ine Level..By Pr| 00000040 6f 67 72 61 6d 6d 65 72 0d 0d 2e 2e 2e 2e 2e 2e |ogrammer........| 00000050 2e 2e 2e 2e 2e 2e 2e 2e 2e 2e 2e 2e 2e 2e 2e 2e |................| * 00000080 2e 2e 2e 2e 2e 0d 0d 0d 50 61 72 74 20 37 3a 20 |........Part 7: | 00000090 4f 70 65 72 61 74 69 6e 67 20 53 79 73 74 65 6d |Operating System| 000000a0 20 43 61 6c 6c 73 20 28 49 49 29 20 2d 20 49 2f | Calls (II) - I/| 000000b0 30 0d 0d 0d 49 6e 20 74 68 69 73 20 73 65 63 6f |0...In this seco| 000000c0 6e 64 20 6c 6f 6f 6b 20 61 74 20 6f 70 65 72 61 |nd look at opera| 000000d0 74 69 6e 67 20 73 79 73 74 65 6d 20 72 6f 75 74 |ting system rout| 000000e0 69 6e 65 73 20 49 27 6c 6c 20 64 65 61 6c 0d 77 |ines I'll deal.w| 000000f0 69 74 68 20 74 68 6f 73 65 20 72 65 6c 61 74 69 |ith those relati| 00000100 6e 67 20 74 6f 20 69 6e 70 75 74 20 61 6e 64 20 |ng to input and | 00000110 6f 75 74 70 75 74 2e 20 20 49 74 27 73 20 6f 6e |output. It's on| 00000120 65 20 6f 66 20 74 68 65 0d 62 65 61 75 74 69 65 |e of the.beautie| 00000130 73 20 6f 66 20 74 68 65 20 42 42 43 20 4d 69 63 |s of the BBC Mic| 00000140 72 6f 20 4f 53 20 74 68 61 74 20 74 68 65 20 72 |ro OS that the r| 00000150 6f 75 74 69 6e 65 73 20 66 6f 72 20 69 6e 70 75 |outines for inpu| 00000160 74 20 61 6e 64 0d 6f 75 74 70 75 74 20 28 49 2f |t and.output (I/| 00000170 4f 29 20 61 72 65 20 69 6e 64 65 70 65 6e 64 65 |O) are independe| 00000180 6e 74 20 6f 66 20 74 68 65 20 73 6f 75 72 63 65 |nt of the source| 00000190 20 6f 72 20 64 65 73 74 69 6e 61 74 69 6f 6e 20 | or destination | 000001a0 6f 66 0d 74 68 61 74 20 49 2f 4f 2e 20 20 54 68 |of.that I/O. Th| 000001b0 65 20 73 65 6c 65 63 74 69 6f 6e 20 6f 66 20 73 |e selection of s| 000001c0 6f 75 72 63 65 20 61 6e 64 20 64 65 73 74 69 6e |ource and destin| 000001d0 61 74 69 6f 6e 20 28 6b 6e 6f 77 6e 20 61 73 0d |ation (known as.| 000001e0 74 68 65 20 69 6e 70 75 74 20 61 6e 64 20 6f 75 |the input and ou| 000001f0 74 70 75 74 20 73 74 72 65 61 6d 29 20 61 72 65 |tput stream) are| 00000200 20 74 68 65 20 70 72 6f 76 69 6e 63 65 20 6f 66 | the province of| 00000210 20 73 6f 6d 65 20 6f 66 20 74 68 65 0d 4f 53 42 | some of the.OSB| 00000220 59 54 45 20 63 61 6c 6c 73 2e 0d 0d 54 6f 20 73 |YTE calls...To s| 00000230 75 6d 6d 61 72 69 73 65 20 74 68 65 20 49 2f 4f |ummarise the I/O| 00000240 20 72 6f 75 74 69 6e 65 73 20 66 69 72 73 74 3a | routines first:| 00000250 0d 0d 49 6e 70 75 74 20 69 73 20 68 61 6e 64 6c |..Input is handl| 00000260 65 64 20 62 79 20 4f 53 52 44 43 48 20 77 68 69 |ed by OSRDCH whi| 00000270 63 68 20 73 74 61 6e 64 73 20 66 6f 72 20 4f 53 |ch stands for OS| 00000280 20 52 65 61 64 0d 43 68 61 72 61 63 74 65 72 0d | Read.Character.| 00000290 0d 4f 75 74 70 75 74 20 69 73 20 68 61 6e 64 6c |.Output is handl| 000002a0 65 64 20 62 79 20 4f 53 57 52 43 48 20 77 68 69 |ed by OSWRCH whi| 000002b0 63 68 20 73 74 61 6e 64 73 20 66 6f 72 20 4f 53 |ch stands for OS| 000002c0 20 57 72 69 74 65 0d 43 68 61 72 61 63 74 65 72 | Write.Character| 000002d0 20 74 6f 67 65 74 68 65 72 20 77 69 74 68 20 74 | together with t| 000002e0 68 65 20 72 65 6c 61 74 65 64 20 63 61 6c 6c 73 |he related calls| 000002f0 20 4f 53 41 53 43 49 20 61 6e 64 20 4f 53 4e 45 | OSASCI and OSNE| 00000300 57 4c 0d 0d 53 65 6c 65 63 74 69 6f 6e 20 6f 66 |WL..Selection of| 00000310 20 73 6f 75 72 63 65 20 69 73 20 62 79 20 75 73 | source is by us| 00000320 69 6e 67 20 4f 53 42 59 54 45 20 32 0d 0d 53 65 |ing OSBYTE 2..Se| 00000330 6c 65 63 74 69 6f 6e 20 6f 66 20 64 65 73 74 69 |lection of desti| 00000340 6e 61 74 69 6f 6e 20 69 73 20 62 79 20 75 73 69 |nation is by usi| 00000350 6e 67 20 4f 53 42 59 54 45 20 33 0d 0d 54 6f 20 |ng OSBYTE 3..To | 00000360 72 65 63 61 70 2c 20 74 68 65 20 4f 53 20 72 6f |recap, the OS ro| 00000370 75 74 69 6e 65 73 20 61 72 65 20 69 6e 20 66 61 |utines are in fa| 00000380 63 74 20 73 75 62 72 6f 75 74 69 6e 65 73 20 65 |ct subroutines e| 00000390 6e 74 65 72 65 64 20 61 74 0d 6b 6e 6f 77 6e 20 |ntered at.known | 000003a0 61 64 64 72 65 73 73 65 73 20 69 6e 20 74 68 65 |addresses in the| 000003b0 20 4f 53 20 52 4f 4d 2e 20 20 54 6f 20 75 73 65 | OS ROM. To use| 000003c0 20 74 68 65 6d 20 74 68 65 20 6e 65 63 65 73 73 | them the necess| 000003d0 61 72 79 0d 76 61 6c 75 65 73 20 66 6f 72 20 74 |ary.values for t| 000003e0 68 65 20 72 65 67 69 73 74 65 72 73 20 61 72 65 |he registers are| 000003f0 20 73 65 74 20 61 6e 64 20 74 68 65 6e 20 79 6f | set and then yo| 00000400 75 20 4a 53 52 20 74 6f 20 74 68 65 0d 72 6f 75 |u JSR to the.rou| 00000410 74 69 6e 65 20 61 6e 64 20 69 74 20 77 69 6c 6c |tine and it will| 00000420 20 52 54 53 20 62 61 63 6b 20 74 6f 20 79 6f 75 | RTS back to you| 00000430 20 77 68 65 6e 20 69 74 73 20 77 6f 72 6b 20 69 | when its work i| 00000440 73 20 64 6f 6e 65 2e 0d 0d 4f 53 52 44 43 48 20 |s done...OSRDCH | 00000450 73 74 61 72 74 73 20 61 74 20 61 64 64 72 65 73 |starts at addres| 00000460 73 20 26 46 46 45 30 20 61 6e 64 20 77 68 65 6e |s &FFE0 and when| 00000470 20 63 61 6c 6c 65 64 20 69 74 20 77 6f 72 6b 73 | called it works| 00000480 0d 72 61 74 68 65 72 20 6c 69 6b 65 20 74 68 65 |.rather like the| 00000490 20 47 45 54 20 66 75 6e 63 74 69 6f 6e 20 69 6e | GET function in| 000004a0 20 42 42 43 20 42 41 53 49 43 2e 20 20 49 74 20 | BBC BASIC. It | 000004b0 77 69 6c 6c 20 77 61 69 74 20 66 6f 72 0d 74 68 |will wait for.th| 000004c0 65 20 6e 65 78 74 20 63 68 61 72 61 63 74 65 72 |e next character| 000004d0 20 74 6f 20 65 6e 74 65 72 20 74 68 65 20 69 6e | to enter the in| 000004e0 70 75 74 20 62 75 66 66 65 72 20 66 6f 72 20 77 |put buffer for w| 000004f0 68 69 63 68 65 76 65 72 0d 73 74 72 65 61 6d 20 |hichever.stream | 00000500 69 73 20 73 65 6c 65 63 74 65 64 20 61 6e 64 20 |is selected and | 00000510 70 75 74 20 69 74 2c 20 6f 72 20 72 61 74 68 65 |put it, or rathe| 00000520 72 20 69 74 73 20 41 53 43 49 49 20 76 61 6c 75 |r its ASCII valu| 00000530 65 2c 0d 69 6e 74 6f 20 74 68 65 20 61 63 63 75 |e,.into the accu| 00000540 6d 75 6c 61 74 6f 72 2e 0d 0d 41 6e 20 65 72 72 |mulator...An err| 00000550 6f 72 20 63 61 6e 20 6f 63 63 75 72 20 77 68 69 |or can occur whi| 00000560 6c 65 20 4f 53 52 44 43 48 20 69 73 20 6f 70 65 |le OSRDCH is ope| 00000570 72 61 74 69 6e 67 2e 20 20 54 68 65 20 6d 6f 73 |rating. The mos| 00000580 74 0d 63 6f 6d 6d 6f 6e 20 69 73 20 61 6e 20 45 |t.common is an E| 00000590 53 43 41 50 45 20 69 6e 20 77 68 69 63 68 20 63 |SCAPE in which c| 000005a0 61 73 65 20 41 20 77 69 6c 6c 20 63 6f 6e 74 61 |ase A will conta| 000005b0 69 6e 20 32 37 20 61 6e 64 20 74 68 65 0d 63 61 |in 27 and the.ca| 000005c0 72 72 79 20 66 6c 61 67 20 77 69 6c 6c 20 62 65 |rry flag will be| 000005d0 20 73 65 74 2c 20 61 73 20 69 74 20 69 73 20 66 | set, as it is f| 000005e0 6f 72 20 61 6e 79 20 65 72 72 6f 72 2e 20 20 41 |or any error. A| 000005f0 6e 20 45 53 43 41 50 45 0d 6d 75 73 74 20 62 65 |n ESCAPE.must be| 00000600 20 61 63 6b 6e 6f 77 6c 65 64 67 65 64 20 62 79 | acknowledged by| 00000610 20 63 61 6c 6c 69 6e 67 20 4f 53 42 59 54 45 20 | calling OSBYTE | 00000620 31 32 36 2e 0d 0d 4f 53 57 52 43 48 20 73 74 61 |126...OSWRCH sta| 00000630 72 74 73 20 61 74 20 61 64 64 72 65 73 73 20 26 |rts at address &| 00000640 46 46 45 45 20 61 6e 64 20 74 61 6b 65 73 20 74 |FFEE and takes t| 00000650 68 65 20 41 53 43 49 49 20 76 61 6c 75 65 20 69 |he ASCII value i| 00000660 6e 0d 74 68 65 20 61 63 63 75 6d 75 6c 61 74 6f |n.the accumulato| 00000670 72 20 61 6e 64 20 73 65 6e 64 73 20 69 74 20 74 |r and sends it t| 00000680 6f 20 74 68 65 20 63 75 72 72 65 6e 74 20 6f 75 |o the current ou| 00000690 74 70 75 74 20 73 74 72 65 61 6d 2e 20 0d 4e 6f |tput stream. .No| 000006a0 74 65 20 74 68 61 74 20 69 66 20 63 65 72 74 61 |te that if certa| 000006b0 69 6e 20 63 6f 6e 74 72 6f 6c 20 63 6f 64 65 73 |in control codes| 000006c0 20 61 72 65 20 73 65 6e 74 20 74 6f 20 74 68 65 | are sent to the| 000006d0 20 56 44 55 0d 64 72 69 76 65 72 73 2c 20 69 2e | VDU.drivers, i.| 000006e0 65 2e 20 74 68 65 20 73 63 72 65 65 6e 2c 20 74 |e. the screen, t| 000006f0 68 65 6e 20 73 6f 6d 65 20 62 79 74 65 73 20 66 |hen some bytes f| 00000700 6f 6c 6c 6f 77 69 6e 67 20 77 69 6c 6c 20 62 65 |ollowing will be| 00000710 0d 69 6e 74 65 72 70 72 65 74 65 64 20 61 73 20 |.interpreted as | 00000720 70 61 72 61 6d 65 74 65 72 73 20 66 6f 72 20 56 |parameters for V| 00000730 44 55 20 63 6f 6d 6d 61 6e 64 73 20 73 75 63 68 |DU commands such| 00000740 20 61 73 20 50 4c 4f 54 20 61 6e 64 0d 54 41 42 | as PLOT and.TAB| 00000750 20 65 71 75 69 76 61 6c 65 6e 74 73 2e 0d 0d 5b | equivalents...[| 00000760 54 68 69 73 20 69 73 20 6e 6f 74 20 74 68 65 20 |This is not the | 00000770 63 61 73 65 20 77 68 65 6e 20 73 65 6e 64 69 6e |case when sendin| 00000780 67 20 74 6f 2c 20 73 61 79 2c 20 61 20 70 72 69 |g to, say, a pri| 00000790 6e 74 65 72 20 6f 6e 6c 79 2c 0d 77 68 65 6e 20 |nter only,.when | 000007a0 61 6c 6c 20 62 79 74 65 73 20 61 72 65 20 70 61 |all bytes are pa| 000007b0 73 73 65 64 20 6f 6e 2e 20 20 54 68 65 72 65 20 |ssed on. There | 000007c0 69 73 20 61 20 64 69 66 66 65 72 65 6e 63 65 20 |is a difference | 000007d0 68 65 72 65 0d 62 65 74 77 65 65 6e 20 74 68 65 |here.between the| 000007e0 20 65 66 66 65 63 74 20 6f 66 20 64 65 66 69 6e | effect of defin| 000007f0 69 6e 67 20 70 72 69 6e 74 65 72 20 61 73 20 74 |ing printer as t| 00000800 68 65 20 6f 6e 6c 79 20 6f 75 74 70 75 74 0d 73 |he only output.s| 00000810 74 72 65 61 6d 20 75 73 69 6e 67 20 4f 53 42 59 |tream using OSBY| 00000820 54 45 20 33 20 61 6e 64 20 70 72 65 66 69 78 69 |TE 3 and prefixi| 00000830 6e 67 20 61 20 73 74 72 69 6e 67 20 6f 66 20 62 |ng a string of b| 00000840 79 74 65 73 20 77 69 74 68 20 61 0d 32 20 28 61 |ytes with a.2 (a| 00000850 73 20 69 6e 20 56 44 55 32 29 20 74 6f 20 73 65 |s in VDU2) to se| 00000860 6c 65 63 74 20 74 68 65 20 70 72 69 6e 74 65 72 |lect the printer| 00000870 2e 20 20 49 6e 20 74 68 65 20 6c 61 74 74 65 72 |. In the latter| 00000880 20 63 61 73 65 0d 74 68 65 20 62 79 74 65 73 20 | case.the bytes | 00000890 61 73 73 6f 63 69 61 74 65 64 20 77 69 74 68 20 |associated with | 000008a0 63 6f 6e 74 72 6f 6c 20 63 6f 64 65 73 20 61 72 |control codes ar| 000008b0 65 20 6e 6f 74 20 73 65 6e 74 2e 5d 0d 0d 54 68 |e not sent.]..Th| 000008c0 65 72 65 20 61 72 65 20 74 77 6f 20 6f 74 68 65 |ere are two othe| 000008d0 72 20 72 6f 75 74 69 6e 65 73 20 72 65 6c 61 74 |r routines relat| 000008e0 65 64 20 74 6f 20 4f 53 57 52 43 48 2e 20 20 4f |ed to OSWRCH. O| 000008f0 53 41 53 43 49 2c 0d 77 68 69 63 68 20 73 74 61 |SASCI,.which sta| 00000900 72 74 73 20 61 74 20 26 46 46 45 33 2c 20 62 65 |rts at &FFE3, be| 00000910 68 61 76 65 73 20 65 78 61 63 74 6c 79 20 61 73 |haves exactly as| 00000920 20 4f 53 57 52 43 48 20 65 78 63 65 70 74 20 77 | OSWRCH except w| 00000930 68 65 6e 0d 74 68 65 20 62 79 74 65 20 70 61 73 |hen.the byte pas| 00000940 73 65 64 20 69 73 20 31 33 20 28 26 30 44 29 20 |sed is 13 (&0D) | 00000950 77 68 69 63 68 20 69 73 20 61 20 63 61 72 72 69 |which is a carri| 00000960 61 67 65 20 72 65 74 75 72 6e 2e 20 20 49 6e 0d |age return. In.| 00000970 74 68 69 73 20 63 61 73 65 20 61 20 6c 69 6e 65 |this case a line| 00000980 20 66 65 65 64 20 28 31 30 20 6f 72 20 26 30 41 | feed (10 or &0A| 00000990 29 20 69 73 20 73 65 6e 74 20 66 6f 6c 6c 6f 77 |) is sent follow| 000009a0 65 64 20 62 79 20 61 0d 63 61 72 72 69 61 67 65 |ed by a.carriage| 000009b0 20 72 65 74 75 72 6e 2e 20 20 49 6e 20 6f 74 68 | return. 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04_12_87/T\OSB07.m1
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04_12_87/T\OSB07.m4
04_12_87/T\OSB07.m5
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