Home » CEEFAX disks » telesoftware16.adl » 10-06-89/Hertz\T
10-06-89/Hertz\T
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 » telesoftware16.adl |
| Filename: | 10-06-89/Hertz\T |
| Read OK: | ✔ |
| File size: | 1048 bytes |
| Load address: | 0000 |
| Exec address: | FFFFFFFF |
File contents
FREQUENCY METER.
Two elements are required to produce a frequency meter. One is a
timer to open a gate to the stream of input pulses for a precise time, and
a counter to sum the number of pulses in that time.
The BBC Computer has a built in timer which is incremented every
10mS and which can be made to generate a special interrupt called an
event, after a preset time. This event has to be enabled by *FX14,5 and
the time interval set by an OSWORD call. In the frequency meter this
interval is set to 1 Second for the low range (0 to 65536 Hz) and 1/10
Second for the high range (64000 to 250000 hz)
The 6522 Versatile Interface Adapter, which provides the printer
and user ports, contains several registers and two 16 bit timer/counters.
One of these (Timer 2) can be made to count pulses input to pin 18 of the
User Port (PB6). The machine code part of the BASIC program HERTZ/B, is
called at each event and reads the count since the start of the previous
interval (initially 1 Second) and then resets the counter to zero, If
there has been more than 2^16 (65536) input pulses counted, the program
changes to the high range with an interval of 1/10 Second. Timer 2 cannot
deal with pulses shorter than 4 micro-seconds, consequently the program
displays 'over-range' if the input rises above 250 Khz. To preserve
accuracy the pulses are summed for ten of the high range intervals ie, 1
Second total, the same as the low range interval.
The interval timer is derived from the Quartz crystal oscillator
inside the machine. It has a fairly good frequency accuracy and does not
drift much after the first half hour after switching on. Fine correction
on the low and high ranges is made in the BASIC program HERTZ/B, lines
1020 and 910 respectively, by means of the ten digit numbers in the
brackets. Yours, of course quite likely, will need to be slightly
different. The low range correction was obtained by picking up the line
scan frequency of a television set receiving a normal TV programme. The
line scan frequency of 15625 Hz exactly can be detected by placing the
amplifier, described below, with its input lead a few inches long close to
the back of the TV set. Do not be tempted to detect the line scan
frequency from your Computer Monitor for this purpose since this is locked
to the machine oscillator. A standard 100KHz Quartz oscillator was used
to determine the correction for the high range, but if the figure is left
at 1.005 etc. the error will still be quite small.
The user port needs normal TTL logic levels as input and reasonably
fast transitions for stability, like any other logic device. Consequently
it is advisable to use an input amplifier that can take LF sine waves and
convert them to fast logic level signals. If the file HERTZ/D is *LOADed
into a MODE 0 screen a circuit diagram of a suitable amplifer, based on
the cheap 4069 CMOS hex-inverter, will be displayed. This will work with
signals as low as 0.1 Vpp at LF but needs about 1 Vpp at the higher
frequencies. It also provides a bias to 0 V if the input falls to zero;
this is required to prevent a false reading of 1Hz at zero frequency
input. The input is diode protected, but should not exceed 6Vpp. The
output and power rails can be connected to the user port via a 20 way IDC
connector and up to 1 metre of flat ribbon cable. The amplifer should be
mounted in a metal box to provide screening, the writer used a tobacco tin
with the lid soldered on.
The BASIC program HERTZ/B contains only legal calls, so it should
work on any BBC computer, but it has only been tested on a BBC-B. The
legal OSBYTE calls do cause some slowing of the machine code, hence the
fairly large correction factor in the high range. This can be improved by
using illegal direct calls to SHIELA as in the alternative BASIC program
Hz/B, but this may not work on all BBC machines or over the TUBE.
HERTZ/T Text File, *TYPE in MODE3.
HERTZ/D Graphics File, *LOAD in MODE0.
HERTZ/B Legal Basic Program.
Hz/B Illegal Basic Program.
P.B.Helsdon 20/4/88
00000000 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | 00000010 20 20 20 20 20 20 20 20 20 46 52 45 51 55 45 4e | FREQUEN| 00000020 43 59 20 4d 45 54 45 52 2e 0d 0d 0d 20 20 20 20 |CY METER.... | 00000030 20 20 20 54 77 6f 20 65 6c 65 6d 65 6e 74 73 20 | Two elements | 00000040 61 72 65 20 72 65 71 75 69 72 65 64 20 74 6f 20 |are required to | 00000050 70 72 6f 64 75 63 65 20 61 20 66 72 65 71 75 65 |produce a freque| 00000060 6e 63 79 20 6d 65 74 65 72 2e 20 20 4f 6e 65 20 |ncy meter. One | 00000070 69 73 20 61 0d 74 69 6d 65 72 20 74 6f 20 6f 70 |is a.timer to op| 00000080 65 6e 20 61 20 67 61 74 65 20 74 6f 20 74 68 65 |en a gate to the| 00000090 20 73 74 72 65 61 6d 20 6f 66 20 69 6e 70 75 74 | stream of input| 000000a0 20 70 75 6c 73 65 73 20 66 6f 72 20 61 20 70 72 | pulses for a pr| 000000b0 65 63 69 73 65 20 74 69 6d 65 2c 20 61 6e 64 0d |ecise time, and.| 000000c0 61 20 63 6f 75 6e 74 65 72 20 74 6f 20 73 75 6d |a counter to sum| 000000d0 20 74 68 65 20 6e 75 6d 62 65 72 20 6f 66 20 70 | the number of p| 000000e0 75 6c 73 65 73 20 69 6e 20 74 68 61 74 20 74 69 |ulses in that ti| 000000f0 6d 65 2e 0d 0d 20 20 20 20 20 20 20 54 68 65 20 |me... The | 00000100 42 42 43 20 43 6f 6d 70 75 74 65 72 20 68 61 73 |BBC Computer has| 00000110 20 61 20 62 75 69 6c 74 20 69 6e 20 74 69 6d 65 | a built in time| 00000120 72 20 77 68 69 63 68 20 69 73 20 69 6e 63 72 65 |r which is incre| 00000130 6d 65 6e 74 65 64 20 65 76 65 72 79 0d 31 30 6d |mented every.10m| 00000140 53 20 61 6e 64 20 77 68 69 63 68 20 63 61 6e 20 |S and which can | 00000150 62 65 20 6d 61 64 65 20 74 6f 20 67 65 6e 65 72 |be made to gener| 00000160 61 74 65 20 61 20 73 70 65 63 69 61 6c 20 69 6e |ate a special in| 00000170 74 65 72 72 75 70 74 20 63 61 6c 6c 65 64 20 61 |terrupt called a| 00000180 6e 0d 65 76 65 6e 74 2c 20 61 66 74 65 72 20 61 |n.event, after a| 00000190 20 70 72 65 73 65 74 20 74 69 6d 65 2e 20 20 54 | preset time. T| 000001a0 68 69 73 20 65 76 65 6e 74 20 68 61 73 20 74 6f |his event has to| 000001b0 20 62 65 20 65 6e 61 62 6c 65 64 20 62 79 20 2a | be enabled by *| 000001c0 46 58 31 34 2c 35 20 61 6e 64 0d 74 68 65 20 74 |FX14,5 and.the t| 000001d0 69 6d 65 20 69 6e 74 65 72 76 61 6c 20 73 65 74 |ime interval set| 000001e0 20 62 79 20 61 6e 20 4f 53 57 4f 52 44 20 63 61 | by an OSWORD ca| 000001f0 6c 6c 2e 20 20 49 6e 20 74 68 65 20 66 72 65 71 |ll. In the freq| 00000200 75 65 6e 63 79 20 6d 65 74 65 72 20 74 68 69 73 |uency meter this| 00000210 0d 69 6e 74 65 72 76 61 6c 20 69 73 20 73 65 74 |.interval is set| 00000220 20 74 6f 20 31 20 53 65 63 6f 6e 64 20 66 6f 72 | to 1 Second for| 00000230 20 74 68 65 20 6c 6f 77 20 72 61 6e 67 65 20 28 | the low range (| 00000240 30 20 74 6f 20 36 35 35 33 36 20 48 7a 29 20 61 |0 to 65536 Hz) a| 00000250 6e 64 20 31 2f 31 30 0d 53 65 63 6f 6e 64 20 66 |nd 1/10.Second f| 00000260 6f 72 20 74 68 65 20 68 69 67 68 20 72 61 6e 67 |or the high rang| 00000270 65 20 28 36 34 30 30 30 20 74 6f 20 32 35 30 30 |e (64000 to 2500| 00000280 30 30 20 68 7a 29 0d 0d 20 20 20 20 20 20 20 54 |00 hz).. T| 00000290 68 65 20 36 35 32 32 20 56 65 72 73 61 74 69 6c |he 6522 Versatil| 000002a0 65 20 49 6e 74 65 72 66 61 63 65 20 41 64 61 70 |e Interface Adap| 000002b0 74 65 72 2c 20 77 68 69 63 68 20 70 72 6f 76 69 |ter, which provi| 000002c0 64 65 73 20 74 68 65 20 70 72 69 6e 74 65 72 0d |des the printer.| 000002d0 61 6e 64 20 75 73 65 72 20 70 6f 72 74 73 2c 20 |and user ports, | 000002e0 63 6f 6e 74 61 69 6e 73 20 73 65 76 65 72 61 6c |contains several| 000002f0 20 72 65 67 69 73 74 65 72 73 20 61 6e 64 20 74 | registers and t| 00000300 77 6f 20 31 36 20 62 69 74 20 74 69 6d 65 72 2f |wo 16 bit timer/| 00000310 63 6f 75 6e 74 65 72 73 2e 20 0d 4f 6e 65 20 6f |counters. .One o| 00000320 66 20 74 68 65 73 65 20 28 54 69 6d 65 72 20 32 |f these (Timer 2| 00000330 29 20 63 61 6e 20 62 65 20 6d 61 64 65 20 74 6f |) can be made to| 00000340 20 63 6f 75 6e 74 20 70 75 6c 73 65 73 20 69 6e | count pulses in| 00000350 70 75 74 20 74 6f 20 70 69 6e 20 31 38 20 6f 66 |put to pin 18 of| 00000360 20 74 68 65 0d 55 73 65 72 20 50 6f 72 74 20 28 | the.User Port (| 00000370 50 42 36 29 2e 20 20 54 68 65 20 6d 61 63 68 69 |PB6). The machi| 00000380 6e 65 20 63 6f 64 65 20 70 61 72 74 20 6f 66 20 |ne code part of | 00000390 74 68 65 20 42 41 53 49 43 20 70 72 6f 67 72 61 |the BASIC progra| 000003a0 6d 20 48 45 52 54 5a 2f 42 2c 20 69 73 0d 63 61 |m HERTZ/B, is.ca| 000003b0 6c 6c 65 64 20 61 74 20 65 61 63 68 20 65 76 65 |lled at each eve| 000003c0 6e 74 20 61 6e 64 20 72 65 61 64 73 20 74 68 65 |nt and reads the| 000003d0 20 63 6f 75 6e 74 20 73 69 6e 63 65 20 74 68 65 | count since the| 000003e0 20 73 74 61 72 74 20 6f 66 20 74 68 65 20 70 72 | start of the pr| 000003f0 65 76 69 6f 75 73 0d 69 6e 74 65 72 76 61 6c 20 |evious.interval | 00000400 28 69 6e 69 74 69 61 6c 6c 79 20 31 20 53 65 63 |(initially 1 Sec| 00000410 6f 6e 64 29 20 61 6e 64 20 74 68 65 6e 20 72 65 |ond) and then re| 00000420 73 65 74 73 20 74 68 65 20 63 6f 75 6e 74 65 72 |sets the counter| 00000430 20 74 6f 20 7a 65 72 6f 2c 20 49 66 0d 74 68 65 | to zero, If.the| 00000440 72 65 20 68 61 73 20 62 65 65 6e 20 6d 6f 72 65 |re has been more| 00000450 20 74 68 61 6e 20 32 5e 31 36 20 28 36 35 35 33 | than 2^16 (6553| 00000460 36 29 20 69 6e 70 75 74 20 70 75 6c 73 65 73 20 |6) input pulses | 00000470 63 6f 75 6e 74 65 64 2c 20 74 68 65 20 70 72 6f |counted, the pro| 00000480 67 72 61 6d 0d 63 68 61 6e 67 65 73 20 74 6f 20 |gram.changes to | 00000490 74 68 65 20 68 69 67 68 20 72 61 6e 67 65 20 77 |the high range w| 000004a0 69 74 68 20 61 6e 20 69 6e 74 65 72 76 61 6c 20 |ith an interval | 000004b0 6f 66 20 31 2f 31 30 20 53 65 63 6f 6e 64 2e 20 |of 1/10 Second. | 000004c0 20 54 69 6d 65 72 20 32 20 63 61 6e 6e 6f 74 0d | Timer 2 cannot.| 000004d0 64 65 61 6c 20 77 69 74 68 20 70 75 6c 73 65 73 |deal with pulses| 000004e0 20 73 68 6f 72 74 65 72 20 74 68 61 6e 20 34 20 | shorter than 4 | 000004f0 6d 69 63 72 6f 2d 73 65 63 6f 6e 64 73 2c 20 63 |micro-seconds, c| 00000500 6f 6e 73 65 71 75 65 6e 74 6c 79 20 74 68 65 20 |onsequently the | 00000510 70 72 6f 67 72 61 6d 0d 64 69 73 70 6c 61 79 73 |program.displays| 00000520 20 27 6f 76 65 72 2d 72 61 6e 67 65 27 20 69 66 | 'over-range' if| 00000530 20 74 68 65 20 69 6e 70 75 74 20 72 69 73 65 73 | the input rises| 00000540 20 61 62 6f 76 65 20 32 35 30 20 4b 68 7a 2e 20 | above 250 Khz. | 00000550 54 6f 20 70 72 65 73 65 72 76 65 0d 61 63 63 75 |To preserve.accu| 00000560 72 61 63 79 20 74 68 65 20 70 75 6c 73 65 73 20 |racy the pulses | 00000570 61 72 65 20 73 75 6d 6d 65 64 20 66 6f 72 20 74 |are summed for t| 00000580 65 6e 20 6f 66 20 74 68 65 20 68 69 67 68 20 72 |en of the high r| 00000590 61 6e 67 65 20 69 6e 74 65 72 76 61 6c 73 20 69 |ange intervals i| 000005a0 65 2c 20 31 0d 53 65 63 6f 6e 64 20 74 6f 74 61 |e, 1.Second tota| 000005b0 6c 2c 20 74 68 65 20 73 61 6d 65 20 61 73 20 74 |l, the same as t| 000005c0 68 65 20 6c 6f 77 20 72 61 6e 67 65 20 69 6e 74 |he low range int| 000005d0 65 72 76 61 6c 2e 0d 0d 20 20 20 20 20 20 20 54 |erval... T| 000005e0 68 65 20 69 6e 74 65 72 76 61 6c 20 74 69 6d 65 |he interval time| 000005f0 72 20 69 73 20 64 65 72 69 76 65 64 20 66 72 6f |r is derived fro| 00000600 6d 20 74 68 65 20 51 75 61 72 74 7a 20 63 72 79 |m the Quartz cry| 00000610 73 74 61 6c 20 6f 73 63 69 6c 6c 61 74 6f 72 0d |stal oscillator.| 00000620 69 6e 73 69 64 65 20 74 68 65 20 6d 61 63 68 69 |inside the machi| 00000630 6e 65 2e 20 49 74 20 68 61 73 20 61 20 66 61 69 |ne. It has a fai| 00000640 72 6c 79 20 67 6f 6f 64 20 66 72 65 71 75 65 6e |rly good frequen| 00000650 63 79 20 61 63 63 75 72 61 63 79 20 61 6e 64 20 |cy accuracy and | 00000660 64 6f 65 73 20 6e 6f 74 0d 64 72 69 66 74 20 6d |does not.drift m| 00000670 75 63 68 20 61 66 74 65 72 20 74 68 65 20 66 69 |uch after the fi| 00000680 72 73 74 20 68 61 6c 66 20 68 6f 75 72 20 61 66 |rst half hour af| 00000690 74 65 72 20 73 77 69 74 63 68 69 6e 67 20 6f 6e |ter switching on| 000006a0 2e 20 20 46 69 6e 65 20 63 6f 72 72 65 63 74 69 |. Fine correcti| 000006b0 6f 6e 0d 6f 6e 20 74 68 65 20 6c 6f 77 20 61 6e |on.on the low an| 000006c0 64 20 68 69 67 68 20 72 61 6e 67 65 73 20 69 73 |d high ranges is| 000006d0 20 6d 61 64 65 20 69 6e 20 74 68 65 20 42 41 53 | made in the BAS| 000006e0 49 43 20 70 72 6f 67 72 61 6d 20 48 45 52 54 5a |IC program HERTZ| 000006f0 2f 42 2c 20 6c 69 6e 65 73 0d 31 30 32 30 20 61 |/B, lines.1020 a| 00000700 6e 64 20 39 31 30 20 72 65 73 70 65 63 74 69 76 |nd 910 respectiv| 00000710 65 6c 79 2c 20 62 79 20 6d 65 61 6e 73 20 6f 66 |ely, by means of| 00000720 20 74 68 65 20 74 65 6e 20 64 69 67 69 74 20 6e | the ten digit n| 00000730 75 6d 62 65 72 73 20 69 6e 20 74 68 65 0d 62 72 |umbers in the.br| 00000740 61 63 6b 65 74 73 2e 20 59 6f 75 72 73 2c 20 6f |ackets. Yours, o| 00000750 66 20 63 6f 75 72 73 65 20 71 75 69 74 65 20 6c |f course quite l| 00000760 69 6b 65 6c 79 2c 20 77 69 6c 6c 20 6e 65 65 64 |ikely, will need| 00000770 20 74 6f 20 62 65 20 73 6c 69 67 68 74 6c 79 0d | to be slightly.| 00000780 64 69 66 66 65 72 65 6e 74 2e 20 20 54 68 65 20 |different. The | 00000790 6c 6f 77 20 72 61 6e 67 65 20 63 6f 72 72 65 63 |low range correc| 000007a0 74 69 6f 6e 20 77 61 73 20 6f 62 74 61 69 6e 65 |tion was obtaine| 000007b0 64 20 62 79 20 70 69 63 6b 69 6e 67 20 75 70 20 |d by picking up | 000007c0 74 68 65 20 6c 69 6e 65 0d 73 63 61 6e 20 66 72 |the line.scan fr| 000007d0 65 71 75 65 6e 63 79 20 6f 66 20 61 20 74 65 6c |equency of a tel| 000007e0 65 76 69 73 69 6f 6e 20 73 65 74 20 72 65 63 65 |evision set rece| 000007f0 69 76 69 6e 67 20 61 20 6e 6f 72 6d 61 6c 20 54 |iving a normal T| 00000800 56 20 70 72 6f 67 72 61 6d 6d 65 2e 20 54 68 65 |V programme. The| 00000810 0d 6c 69 6e 65 20 73 63 61 6e 20 66 72 65 71 75 |.line scan frequ| 00000820 65 6e 63 79 20 6f 66 20 31 35 36 32 35 20 48 7a |ency of 15625 Hz| 00000830 20 65 78 61 63 74 6c 79 20 63 61 6e 20 62 65 20 | exactly can be | 00000840 64 65 74 65 63 74 65 64 20 62 79 20 70 6c 61 63 |detected by plac| 00000850 69 6e 67 20 74 68 65 0d 61 6d 70 6c 69 66 69 65 |ing the.amplifie| 00000860 72 2c 20 64 65 73 63 72 69 62 65 64 20 62 65 6c |r, described bel| 00000870 6f 77 2c 20 77 69 74 68 20 69 74 73 20 69 6e 70 |ow, with its inp| 00000880 75 74 20 6c 65 61 64 20 61 20 66 65 77 20 69 6e |ut lead a few in| 00000890 63 68 65 73 20 6c 6f 6e 67 20 63 6c 6f 73 65 20 |ches long close | 000008a0 74 6f 0d 74 68 65 20 62 61 63 6b 20 6f 66 20 74 |to.the back of t| 000008b0 68 65 20 54 56 20 73 65 74 2e 20 20 44 6f 20 6e |he TV set. Do n| 000008c0 6f 74 20 62 65 20 74 65 6d 70 74 65 64 20 74 6f |ot be tempted to| 000008d0 20 64 65 74 65 63 74 20 74 68 65 20 6c 69 6e 65 | detect the line| 000008e0 20 73 63 61 6e 0d 66 72 65 71 75 65 6e 63 79 20 | scan.frequency | 000008f0 66 72 6f 6d 20 79 6f 75 72 20 43 6f 6d 70 75 74 |from your Comput| 00000900 65 72 20 4d 6f 6e 69 74 6f 72 20 66 6f 72 20 74 |er Monitor for t| 00000910 68 69 73 20 70 75 72 70 6f 73 65 20 73 69 6e 63 |his purpose sinc| 00000920 65 20 74 68 69 73 20 69 73 20 6c 6f 63 6b 65 64 |e this is locked| 00000930 0d 74 6f 20 74 68 65 20 6d 61 63 68 69 6e 65 20 |.to the machine | 00000940 6f 73 63 69 6c 6c 61 74 6f 72 2e 20 20 41 20 73 |oscillator. A s| 00000950 74 61 6e 64 61 72 64 20 31 30 30 4b 48 7a 20 51 |tandard 100KHz Q| 00000960 75 61 72 74 7a 20 6f 73 63 69 6c 6c 61 74 6f 72 |uartz oscillator| 00000970 20 77 61 73 20 75 73 65 64 0d 74 6f 20 64 65 74 | was used.to det| 00000980 65 72 6d 69 6e 65 20 74 68 65 20 63 6f 72 72 65 |ermine the corre| 00000990 63 74 69 6f 6e 20 66 6f 72 20 74 68 65 20 68 69 |ction for the hi| 000009a0 67 68 20 72 61 6e 67 65 2c 20 62 75 74 20 69 66 |gh range, but if| 000009b0 20 74 68 65 20 66 69 67 75 72 65 20 69 73 20 6c | the figure is l| 000009c0 65 66 74 0d 61 74 20 31 2e 30 30 35 20 65 74 63 |eft.at 1.005 etc| 000009d0 2e 20 74 68 65 20 65 72 72 6f 72 20 77 69 6c 6c |. the error will| 000009e0 20 73 74 69 6c 6c 20 62 65 20 71 75 69 74 65 20 | still be quite | 000009f0 73 6d 61 6c 6c 2e 0d 0d 20 20 20 20 20 20 20 54 |small... T| 00000a00 68 65 20 75 73 65 72 20 70 6f 72 74 20 6e 65 65 |he user port nee| 00000a10 64 73 20 6e 6f 72 6d 61 6c 20 54 54 4c 20 6c 6f |ds normal TTL lo| 00000a20 67 69 63 20 6c 65 76 65 6c 73 20 61 73 20 69 6e |gic levels as in| 00000a30 70 75 74 20 61 6e 64 20 72 65 61 73 6f 6e 61 62 |put and reasonab| 00000a40 6c 79 0d 66 61 73 74 20 74 72 61 6e 73 69 74 69 |ly.fast transiti| 00000a50 6f 6e 73 20 66 6f 72 20 73 74 61 62 69 6c 69 74 |ons for stabilit| 00000a60 79 2c 20 6c 69 6b 65 20 61 6e 79 20 6f 74 68 65 |y, like any othe| 00000a70 72 20 6c 6f 67 69 63 20 64 65 76 69 63 65 2e 20 |r logic device. | 00000a80 20 43 6f 6e 73 65 71 75 65 6e 74 6c 79 0d 69 74 | Consequently.it| 00000a90 20 69 73 20 61 64 76 69 73 61 62 6c 65 20 74 6f | is advisable to| 00000aa0 20 75 73 65 20 61 6e 20 69 6e 70 75 74 20 61 6d | use an input am| 00000ab0 70 6c 69 66 69 65 72 20 74 68 61 74 20 63 61 6e |plifier that can| 00000ac0 20 74 61 6b 65 20 4c 46 20 73 69 6e 65 20 77 61 | take LF sine wa| 00000ad0 76 65 73 20 61 6e 64 0d 63 6f 6e 76 65 72 74 20 |ves and.convert | 00000ae0 74 68 65 6d 20 74 6f 20 66 61 73 74 20 6c 6f 67 |them to fast log| 00000af0 69 63 20 6c 65 76 65 6c 20 73 69 67 6e 61 6c 73 |ic level signals| 00000b00 2e 20 20 49 66 20 74 68 65 20 66 69 6c 65 20 48 |. If the file H| 00000b10 45 52 54 5a 2f 44 20 69 73 20 2a 4c 4f 41 44 65 |ERTZ/D is *LOADe| 00000b20 64 0d 69 6e 74 6f 20 61 20 4d 4f 44 45 20 30 20 |d.into a MODE 0 | 00000b30 73 63 72 65 65 6e 20 61 20 63 69 72 63 75 69 74 |screen a circuit| 00000b40 20 64 69 61 67 72 61 6d 20 6f 66 20 61 20 73 75 | diagram of a su| 00000b50 69 74 61 62 6c 65 20 61 6d 70 6c 69 66 65 72 2c |itable amplifer,| 00000b60 20 62 61 73 65 64 20 6f 6e 0d 74 68 65 20 63 68 | based on.the ch| 00000b70 65 61 70 20 34 30 36 39 20 43 4d 4f 53 20 68 65 |eap 4069 CMOS he| 00000b80 78 2d 69 6e 76 65 72 74 65 72 2c 20 77 69 6c 6c |x-inverter, will| 00000b90 20 62 65 20 64 69 73 70 6c 61 79 65 64 2e 20 20 | be displayed. | 00000ba0 54 68 69 73 20 77 69 6c 6c 20 77 6f 72 6b 20 77 |This will work w| 00000bb0 69 74 68 0d 73 69 67 6e 61 6c 73 20 61 73 20 6c |ith.signals as l| 00000bc0 6f 77 20 61 73 20 30 2e 31 20 56 70 70 20 61 74 |ow as 0.1 Vpp at| 00000bd0 20 4c 46 20 62 75 74 20 6e 65 65 64 73 20 61 62 | LF but needs ab| 00000be0 6f 75 74 20 31 20 56 70 70 20 61 74 20 74 68 65 |out 1 Vpp at the| 00000bf0 20 68 69 67 68 65 72 0d 66 72 65 71 75 65 6e 63 | higher.frequenc| 00000c00 69 65 73 2e 20 49 74 20 61 6c 73 6f 20 70 72 6f |ies. It also pro| 00000c10 76 69 64 65 73 20 61 20 62 69 61 73 20 74 6f 20 |vides a bias to | 00000c20 30 20 56 20 69 66 20 74 68 65 20 69 6e 70 75 74 |0 V if the input| 00000c30 20 66 61 6c 6c 73 20 74 6f 20 7a 65 72 6f 3b 0d | falls to zero;.| 00000c40 74 68 69 73 20 69 73 20 72 65 71 75 69 72 65 64 |this is required| 00000c50 20 74 6f 20 70 72 65 76 65 6e 74 20 61 20 66 61 | to prevent a fa| 00000c60 6c 73 65 20 72 65 61 64 69 6e 67 20 6f 66 20 31 |lse reading of 1| 00000c70 48 7a 20 61 74 20 7a 65 72 6f 20 66 72 65 71 75 |Hz at zero frequ| 00000c80 65 6e 63 79 0d 69 6e 70 75 74 2e 20 20 54 68 65 |ency.input. The| 00000c90 20 69 6e 70 75 74 20 69 73 20 64 69 6f 64 65 20 | input is diode | 00000ca0 70 72 6f 74 65 63 74 65 64 2c 20 62 75 74 20 73 |protected, but s| 00000cb0 68 6f 75 6c 64 20 6e 6f 74 20 65 78 63 65 65 64 |hould not exceed| 00000cc0 20 36 56 70 70 2e 20 20 54 68 65 0d 6f 75 74 70 | 6Vpp. The.outp| 00000cd0 75 74 20 61 6e 64 20 70 6f 77 65 72 20 72 61 69 |ut and power rai| 00000ce0 6c 73 20 63 61 6e 20 62 65 20 63 6f 6e 6e 65 63 |ls can be connec| 00000cf0 74 65 64 20 74 6f 20 74 68 65 20 75 73 65 72 20 |ted to the user | 00000d00 70 6f 72 74 20 76 69 61 20 61 20 32 30 20 77 61 |port via a 20 wa| 00000d10 79 20 49 44 43 0d 63 6f 6e 6e 65 63 74 6f 72 20 |y IDC.connector | 00000d20 61 6e 64 20 75 70 20 74 6f 20 31 20 6d 65 74 72 |and up to 1 metr| 00000d30 65 20 6f 66 20 66 6c 61 74 20 72 69 62 62 6f 6e |e of flat ribbon| 00000d40 20 63 61 62 6c 65 2e 20 20 54 68 65 20 61 6d 70 | cable. The amp| 00000d50 6c 69 66 65 72 20 73 68 6f 75 6c 64 20 62 65 0d |lifer should be.| 00000d60 6d 6f 75 6e 74 65 64 20 69 6e 20 61 20 6d 65 74 |mounted in a met| 00000d70 61 6c 20 62 6f 78 20 74 6f 20 70 72 6f 76 69 64 |al box to provid| 00000d80 65 20 73 63 72 65 65 6e 69 6e 67 2c 20 74 68 65 |e screening, the| 00000d90 20 77 72 69 74 65 72 20 75 73 65 64 20 61 20 74 | writer used a t| 00000da0 6f 62 61 63 63 6f 20 74 69 6e 0d 77 69 74 68 20 |obacco tin.with | 00000db0 74 68 65 20 6c 69 64 20 73 6f 6c 64 65 72 65 64 |the lid soldered| 00000dc0 20 6f 6e 2e 0d 0d 20 20 20 20 20 20 20 54 68 65 | on... The| 00000dd0 20 42 41 53 49 43 20 70 72 6f 67 72 61 6d 20 48 | BASIC program H| 00000de0 45 52 54 5a 2f 42 20 63 6f 6e 74 61 69 6e 73 20 |ERTZ/B contains | 00000df0 6f 6e 6c 79 20 6c 65 67 61 6c 20 63 61 6c 6c 73 |only legal calls| 00000e00 2c 20 73 6f 20 69 74 20 73 68 6f 75 6c 64 0d 77 |, so it should.w| 00000e10 6f 72 6b 20 6f 6e 20 61 6e 79 20 42 42 43 20 63 |ork on any BBC c| 00000e20 6f 6d 70 75 74 65 72 2c 20 62 75 74 20 69 74 20 |omputer, but it | 00000e30 68 61 73 20 6f 6e 6c 79 20 62 65 65 6e 20 74 65 |has only been te| 00000e40 73 74 65 64 20 6f 6e 20 61 20 42 42 43 2d 42 2e |sted on a BBC-B.| 00000e50 20 54 68 65 0d 6c 65 67 61 6c 20 4f 53 42 59 54 | The.legal OSBYT| 00000e60 45 20 63 61 6c 6c 73 20 64 6f 20 63 61 75 73 65 |E calls do cause| 00000e70 20 73 6f 6d 65 20 73 6c 6f 77 69 6e 67 20 6f 66 | some slowing of| 00000e80 20 74 68 65 20 6d 61 63 68 69 6e 65 20 63 6f 64 | the machine cod| 00000e90 65 2c 20 68 65 6e 63 65 20 74 68 65 0d 66 61 69 |e, hence the.fai| 00000ea0 72 6c 79 20 6c 61 72 67 65 20 63 6f 72 72 65 63 |rly large correc| 00000eb0 74 69 6f 6e 20 66 61 63 74 6f 72 20 69 6e 20 74 |tion factor in t| 00000ec0 68 65 20 68 69 67 68 20 72 61 6e 67 65 2e 20 54 |he high range. T| 00000ed0 68 69 73 20 63 61 6e 20 62 65 20 69 6d 70 72 6f |his can be impro| 00000ee0 76 65 64 20 62 79 0d 75 73 69 6e 67 20 69 6c 6c |ved by.using ill| 00000ef0 65 67 61 6c 20 64 69 72 65 63 74 20 63 61 6c 6c |egal direct call| 00000f00 73 20 74 6f 20 53 48 49 45 4c 41 20 61 73 20 69 |s to SHIELA as i| 00000f10 6e 20 74 68 65 20 61 6c 74 65 72 6e 61 74 69 76 |n the alternativ| 00000f20 65 20 42 41 53 49 43 20 70 72 6f 67 72 61 6d 0d |e BASIC program.| 00000f30 48 7a 2f 42 2c 20 62 75 74 20 74 68 69 73 20 6d |Hz/B, but this m| 00000f40 61 79 20 6e 6f 74 20 77 6f 72 6b 20 6f 6e 20 61 |ay not work on a| 00000f50 6c 6c 20 42 42 43 20 6d 61 63 68 69 6e 65 73 20 |ll BBC machines | 00000f60 6f 72 20 6f 76 65 72 20 74 68 65 20 54 55 42 45 |or over the TUBE| 00000f70 2e 0d 0d 0d 20 48 45 52 54 5a 2f 54 20 54 65 78 |.... HERTZ/T Tex| 00000f80 74 20 46 69 6c 65 2c 20 2a 54 59 50 45 20 69 6e |t File, *TYPE in| 00000f90 20 4d 4f 44 45 33 2e 0d 20 48 45 52 54 5a 2f 44 | MODE3.. HERTZ/D| 00000fa0 20 47 72 61 70 68 69 63 73 20 46 69 6c 65 2c 20 | Graphics File, | 00000fb0 2a 4c 4f 41 44 20 69 6e 20 4d 4f 44 45 30 2e 0d |*LOAD in MODE0..| 00000fc0 20 48 45 52 54 5a 2f 42 20 4c 65 67 61 6c 20 42 | HERTZ/B Legal B| 00000fd0 61 73 69 63 20 50 72 6f 67 72 61 6d 2e 0d 20 48 |asic Program.. H| 00000fe0 7a 2f 42 20 20 20 20 49 6c 6c 65 67 61 6c 20 42 |z/B Illegal B| 00000ff0 61 73 69 63 20 50 72 6f 67 72 61 6d 2e 0d 20 20 |asic Program.. | 00001000 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 | | * 00001030 20 20 20 20 50 2e 42 2e 48 65 6c 73 64 6f 6e 20 | P.B.Helsdon | 00001040 32 30 2f 34 2f 38 38 0d |20/4/88.| 00001048
10-06-89/Hertz\T.m0
10-06-89/Hertz\T.m1
10-06-89/Hertz\T.m2
10-06-89/Hertz\T.m4
10-06-89/Hertz\T.m5
.