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80 column text only file 
  
Eprom Emulator Instructions  
===========================  
If you don't have access to a ROM  board  with  sideways  RAM socket(s)  
but,like me,have access to an Eprom programmer then you could build this  
little device.  
  
It need not only be restricted to storing sideways ROM images,but may be  
used with other Eprom based devices that need to be continu ally  
redeveloped - for example it can also be used with Maplin's UM5100 speech  
programmer replay only board,which accepts Eproms onl y.  
  
PARTS...  
The circuit diagram shows electrically how to assemble the unit,requiring  
the following parts:  
  
1x  62256 SRAM (28 pin)  
1x  28 pin DIL socket  
1x  SPDT switch  
1x  Battery box to hold 3xAA batteries  
2x  IN4001 diodes  
  
In addition,it may be useful to have a ZIF socket mounted on the outside  
of your case,to reduce the stress on,levering the device in and out.  
  
BENEFITS...  
*Switches automatically between battery backup and system powersupply  
*Can emulate chips 27128/27256  
*Low power CMOS static RAM lasts for weeks on a set of batteries  
*Cheaper than EEPROM (around `22)  
*Hardware selection of write enable/write protect - gets around protected  
 ROM images  
  
BUILD...  
1.As the pin outs on a 62256 and 27128 (or 27256) are virtually identical  
all but print 1,27,28 can be direct one to one connections .  
2.Pin 1,27,28 can be bent out of shape carefully with a pair of pliers -  
being carefully not to stress the metal.  
3.Solder a small wire to pin 1 and run this under the chip and plug it  
into pin 27 of the socket.This becomes address 14.  
4.Not CS and Not OE are handled by the Eprom programmer or microprocessor  
so can be left aline.  
5.Having bent pin 27 out of the way of the small wire you just soldered on  
attach this to the centre pole of the switch.The other tw o terminals of  
the switch go to pin 14 (GND) and 28 (VCC).  
6.Pin 28 also must be split.The two diodes prevent the microprocessor's  
power supply from trying to recharge the batteries,and vice  versa.  
7.The battery clip and switch should be wire ended and insulated to  
prevent shorts in confined spaces and to allow the device to fit  
 under the keyboard on a BBC B.  
  
HINTS...  
*Below around 2.5v the contents of SRAM may become corrupted or lost  
*I found this very useful to test out the suitability of ROM images before  
 committing them to EPROM  
*I also fitted a ZIF socket to the ashtray (the punch out section on the  
 left of the B's keyboard where the speech sockets would go)  
 to save having to keep levering the pack in and out  
*If you do make a ZIF socket,there may be timing problems with piggy back  
 ROMs such as Mega 3.Try connecting a 100nF capacitor from  pin 28 to pin  
 14.  
*The auto power switching only works if there is a difference of around  
 0.6v between the main power supply and the battery pack - he nce the use  
 of 4.5v of cells in the battery  
  
FROM...  
Robert Sprowson.  
(01625) 431067.  
Happy soldering! 

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00000050  45 70 72 6f 6d 20 45 6d  75 6c 61 74 6f 72 22 3a  |Eprom Emulator":|
00000060  f4 20 4d 61 6b 65 20 77  61 79 20 66 6f 72 20 6d  |. Make way for m|
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000000a0  45 4d 55 4c 41 54 45 22  3a d9 23 46 3a f4 20 54  |EMULATE":.#F:. T|
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000000d0  32 1b e7 46 3d 30 20 8c  f2 69 6e 73 74 61 6c 6c  |2..F=0 ..install|
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00000130  a6 28 31 35 30 29 3a f9  0d 00 64 06 e1 20 0d 00  |.(150):...d.. ..|
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00000150  f1 3a f5 20 0d 00 82 39  f1 22 49 6e 73 65 72 74  |.:. ...9."Insert|
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00000340  41 4d 22 20 0d 01 04 14  f1 22 32 29 20 52 45 41  |AM" ....."2) REA|
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000003b0  0d 01 36 36 e7 41 3d 32  20 8c ef 26 31 36 2c 30  |..66.A=2 ..&16,0|
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000003d0  45 4d 55 54 58 54 31 22  3a 5a 3d a5 3a ef 26 31  |EMUTXT1":Z=.:.&1|
000003e0  36 2c 34 2c 31 35 0d 01  40 1d db 3a f1 22 45 70  |6,4,15..@..:."Ep|
000003f0  72 6f 6d 20 45 6d 75 6c  61 74 6f 72 22 3a 46 3d  |rom Emulator":F=|
00000400  b9 3a e1 0d ff 20 20 0d  38 30 20 63 6f 6c 75 6d  |.:...  .80 colum|
00000410  6e 20 74 65 78 74 20 6f  6e 6c 79 20 66 69 6c 65  |n text only file|
00000420  20 0d 20 20 0d 45 70 72  6f 6d 20 45 6d 75 6c 61  | .  .Eprom Emula|
00000430  74 6f 72 20 49 6e 73 74  72 75 63 74 69 6f 6e 73  |tor Instructions|
00000440  20 20 0d 3d 3d 3d 3d 3d  3d 3d 3d 3d 3d 3d 3d 3d  |  .=============|
00000450  3d 3d 3d 3d 3d 3d 3d 3d  3d 3d 3d 3d 3d 3d 20 20  |==============  |
00000460  0d 49 66 20 79 6f 75 20  64 6f 6e 27 74 20 68 61  |.If you don't ha|
00000470  76 65 20 61 63 63 65 73  73 20 74 6f 20 61 20 52  |ve access to a R|
00000480  4f 4d 20 20 62 6f 61 72  64 20 20 77 69 74 68 20  |OM  board  with |
00000490  20 73 69 64 65 77 61 79  73 20 20 52 41 4d 20 73  | sideways  RAM s|
000004a0  6f 63 6b 65 74 28 73 29  20 20 0d 62 75 74 2c 6c  |ocket(s)  .but,l|
000004b0  69 6b 65 20 6d 65 2c 68  61 76 65 20 61 63 63 65  |ike me,have acce|
000004c0  73 73 20 74 6f 20 61 6e  20 45 70 72 6f 6d 20 70  |ss to an Eprom p|
000004d0  72 6f 67 72 61 6d 6d 65  72 20 74 68 65 6e 20 79  |rogrammer then y|
000004e0  6f 75 20 63 6f 75 6c 64  20 62 75 69 6c 64 20 74  |ou could build t|
000004f0  68 69 73 20 20 0d 6c 69  74 74 6c 65 20 64 65 76  |his  .little dev|
00000500  69 63 65 2e 20 20 0d 20  20 0d 49 74 20 6e 65 65  |ice.  .  .It nee|
00000510  64 20 6e 6f 74 20 6f 6e  6c 79 20 62 65 20 72 65  |d not only be re|
00000520  73 74 72 69 63 74 65 64  20 74 6f 20 73 74 6f 72  |stricted to stor|
00000530  69 6e 67 20 73 69 64 65  77 61 79 73 20 52 4f 4d  |ing sideways ROM|
00000540  20 69 6d 61 67 65 73 2c  62 75 74 20 6d 61 79 20  | images,but may |
00000550  62 65 20 20 0d 75 73 65  64 20 77 69 74 68 20 6f  |be  .used with o|
00000560  74 68 65 72 20 45 70 72  6f 6d 20 62 61 73 65 64  |ther Eprom based|
00000570  20 64 65 76 69 63 65 73  20 74 68 61 74 20 6e 65  | devices that ne|
00000580  65 64 20 74 6f 20 62 65  20 63 6f 6e 74 69 6e 75  |ed to be continu|
00000590  20 61 6c 6c 79 20 20 0d  72 65 64 65 76 65 6c 6f  | ally  .redevelo|
000005a0  70 65 64 20 2d 20 66 6f  72 20 65 78 61 6d 70 6c  |ped - for exampl|
000005b0  65 20 69 74 20 63 61 6e  20 61 6c 73 6f 20 62 65  |e it can also be|
000005c0  20 75 73 65 64 20 77 69  74 68 20 4d 61 70 6c 69  | used with Mapli|
000005d0  6e 27 73 20 55 4d 35 31  30 30 20 73 70 65 65 63  |n's UM5100 speec|
000005e0  68 20 20 0d 70 72 6f 67  72 61 6d 6d 65 72 20 72  |h  .programmer r|
000005f0  65 70 6c 61 79 20 6f 6e  6c 79 20 62 6f 61 72 64  |eplay only board|
00000600  2c 77 68 69 63 68 20 61  63 63 65 70 74 73 20 45  |,which accepts E|
00000610  70 72 6f 6d 73 20 6f 6e  6c 20 79 2e 20 20 0d 20  |proms onl y.  . |
00000620  20 0d 50 41 52 54 53 2e  2e 2e 20 20 0d 54 68 65  | .PARTS...  .The|
00000630  20 63 69 72 63 75 69 74  20 64 69 61 67 72 61 6d  | circuit diagram|
00000640  20 73 68 6f 77 73 20 65  6c 65 63 74 72 69 63 61  | shows electrica|
00000650  6c 6c 79 20 68 6f 77 20  74 6f 20 61 73 73 65 6d  |lly how to assem|
00000660  62 6c 65 20 74 68 65 20  75 6e 69 74 2c 72 65 71  |ble the unit,req|
00000670  75 69 72 69 6e 67 20 20  0d 74 68 65 20 66 6f 6c  |uiring  .the fol|
00000680  6c 6f 77 69 6e 67 20 70  61 72 74 73 3a 20 20 0d  |lowing parts:  .|
00000690  20 20 0d 31 78 20 20 36  32 32 35 36 20 53 52 41  |  .1x  62256 SRA|
000006a0  4d 20 28 32 38 20 70 69  6e 29 20 20 0d 31 78 20  |M (28 pin)  .1x |
000006b0  20 32 38 20 70 69 6e 20  44 49 4c 20 73 6f 63 6b  | 28 pin DIL sock|
000006c0  65 74 20 20 0d 31 78 20  20 53 50 44 54 20 73 77  |et  .1x  SPDT sw|
000006d0  69 74 63 68 20 20 0d 31  78 20 20 42 61 74 74 65  |itch  .1x  Batte|
000006e0  72 79 20 62 6f 78 20 74  6f 20 68 6f 6c 64 20 33  |ry box to hold 3|
000006f0  78 41 41 20 62 61 74 74  65 72 69 65 73 20 20 0d  |xAA batteries  .|
00000700  32 78 20 20 49 4e 34 30  30 31 20 64 69 6f 64 65  |2x  IN4001 diode|
00000710  73 20 20 0d 20 20 0d 49  6e 20 61 64 64 69 74 69  |s  .  .In additi|
00000720  6f 6e 2c 69 74 20 6d 61  79 20 62 65 20 75 73 65  |on,it may be use|
00000730  66 75 6c 20 74 6f 20 68  61 76 65 20 61 20 5a 49  |ful to have a ZI|
00000740  46 20 73 6f 63 6b 65 74  20 6d 6f 75 6e 74 65 64  |F socket mounted|
00000750  20 6f 6e 20 74 68 65 20  6f 75 74 73 69 64 65 20  | on the outside |
00000760  20 0d 6f 66 20 79 6f 75  72 20 63 61 73 65 2c 74  | .of your case,t|
00000770  6f 20 72 65 64 75 63 65  20 74 68 65 20 73 74 72  |o reduce the str|
00000780  65 73 73 20 6f 6e 2c 6c  65 76 65 72 69 6e 67 20  |ess on,levering |
00000790  74 68 65 20 64 65 76 69  63 65 20 69 6e 20 61 6e  |the device in an|
000007a0  64 20 6f 75 74 2e 20 20  0d 20 20 0d 42 45 4e 45  |d out.  .  .BENE|
000007b0  46 49 54 53 2e 2e 2e 20  20 0d 2a 53 77 69 74 63  |FITS...  .*Switc|
000007c0  68 65 73 20 61 75 74 6f  6d 61 74 69 63 61 6c 6c  |hes automaticall|
000007d0  79 20 62 65 74 77 65 65  6e 20 62 61 74 74 65 72  |y between batter|
000007e0  79 20 62 61 63 6b 75 70  20 61 6e 64 20 73 79 73  |y backup and sys|
000007f0  74 65 6d 20 70 6f 77 65  72 73 75 70 70 6c 79 20  |tem powersupply |
00000800  20 0d 2a 43 61 6e 20 65  6d 75 6c 61 74 65 20 63  | .*Can emulate c|
00000810  68 69 70 73 20 32 37 31  32 38 2f 32 37 32 35 36  |hips 27128/27256|
00000820  20 20 0d 2a 4c 6f 77 20  70 6f 77 65 72 20 43 4d  |  .*Low power CM|
00000830  4f 53 20 73 74 61 74 69  63 20 52 41 4d 20 6c 61  |OS static RAM la|
00000840  73 74 73 20 66 6f 72 20  77 65 65 6b 73 20 6f 6e  |sts for weeks on|
00000850  20 61 20 73 65 74 20 6f  66 20 62 61 74 74 65 72  | a set of batter|
00000860  69 65 73 20 20 0d 2a 43  68 65 61 70 65 72 20 74  |ies  .*Cheaper t|
00000870  68 61 6e 20 45 45 50 52  4f 4d 20 28 61 72 6f 75  |han EEPROM (arou|
00000880  6e 64 20 60 32 32 29 20  20 0d 2a 48 61 72 64 77  |nd `22)  .*Hardw|
00000890  61 72 65 20 73 65 6c 65  63 74 69 6f 6e 20 6f 66  |are selection of|
000008a0  20 77 72 69 74 65 20 65  6e 61 62 6c 65 2f 77 72  | write enable/wr|
000008b0  69 74 65 20 70 72 6f 74  65 63 74 20 2d 20 67 65  |ite protect - ge|
000008c0  74 73 20 61 72 6f 75 6e  64 20 70 72 6f 74 65 63  |ts around protec|
000008d0  74 65 64 20 20 0d 20 52  4f 4d 20 69 6d 61 67 65  |ted  . ROM image|
000008e0  73 20 20 0d 20 20 0d 42  55 49 4c 44 2e 2e 2e 20  |s  .  .BUILD... |
000008f0  20 0d 31 2e 41 73 20 74  68 65 20 70 69 6e 20 6f  | .1.As the pin o|
00000900  75 74 73 20 6f 6e 20 61  20 36 32 32 35 36 20 61  |uts on a 62256 a|
00000910  6e 64 20 32 37 31 32 38  20 28 6f 72 20 32 37 32  |nd 27128 (or 272|
00000920  35 36 29 20 61 72 65 20  76 69 72 74 75 61 6c 6c  |56) are virtuall|
00000930  79 20 69 64 65 6e 74 69  63 61 6c 20 20 0d 61 6c  |y identical  .al|
00000940  6c 20 62 75 74 20 70 72  69 6e 74 20 31 2c 32 37  |l but print 1,27|
00000950  2c 32 38 20 63 61 6e 20  62 65 20 64 69 72 65 63  |,28 can be direc|
00000960  74 20 6f 6e 65 20 74 6f  20 6f 6e 65 20 63 6f 6e  |t one to one con|
00000970  6e 65 63 74 69 6f 6e 73  20 2e 20 20 0d 32 2e 50  |nections .  .2.P|
00000980  69 6e 20 31 2c 32 37 2c  32 38 20 63 61 6e 20 62  |in 1,27,28 can b|
00000990  65 20 62 65 6e 74 20 6f  75 74 20 6f 66 20 73 68  |e bent out of sh|
000009a0  61 70 65 20 63 61 72 65  66 75 6c 6c 79 20 77 69  |ape carefully wi|
000009b0  74 68 20 61 20 70 61 69  72 20 6f 66 20 70 6c 69  |th a pair of pli|
000009c0  65 72 73 20 2d 20 20 0d  62 65 69 6e 67 20 63 61  |ers -  .being ca|
000009d0  72 65 66 75 6c 6c 79 20  6e 6f 74 20 74 6f 20 73  |refully not to s|
000009e0  74 72 65 73 73 20 74 68  65 20 6d 65 74 61 6c 2e  |tress the metal.|
000009f0  20 20 0d 33 2e 53 6f 6c  64 65 72 20 61 20 73 6d  |  .3.Solder a sm|
00000a00  61 6c 6c 20 77 69 72 65  20 74 6f 20 70 69 6e 20  |all wire to pin |
00000a10  31 20 61 6e 64 20 72 75  6e 20 74 68 69 73 20 75  |1 and run this u|
00000a20  6e 64 65 72 20 74 68 65  20 63 68 69 70 20 61 6e  |nder the chip an|
00000a30  64 20 70 6c 75 67 20 69  74 20 20 0d 69 6e 74 6f  |d plug it  .into|
00000a40  20 70 69 6e 20 32 37 20  6f 66 20 74 68 65 20 73  | pin 27 of the s|
00000a50  6f 63 6b 65 74 2e 54 68  69 73 20 62 65 63 6f 6d  |ocket.This becom|
00000a60  65 73 20 61 64 64 72 65  73 73 20 31 34 2e 20 20  |es address 14.  |
00000a70  0d 34 2e 4e 6f 74 20 43  53 20 61 6e 64 20 4e 6f  |.4.Not CS and No|
00000a80  74 20 4f 45 20 61 72 65  20 68 61 6e 64 6c 65 64  |t OE are handled|
00000a90  20 62 79 20 74 68 65 20  45 70 72 6f 6d 20 70 72  | by the Eprom pr|
00000aa0  6f 67 72 61 6d 6d 65 72  20 6f 72 20 6d 69 63 72  |ogrammer or micr|
00000ab0  6f 70 72 6f 63 65 73 73  6f 72 20 20 0d 73 6f 20  |oprocessor  .so |
00000ac0  63 61 6e 20 62 65 20 6c  65 66 74 20 61 6c 69 6e  |can be left alin|
00000ad0  65 2e 20 20 0d 35 2e 48  61 76 69 6e 67 20 62 65  |e.  .5.Having be|
00000ae0  6e 74 20 70 69 6e 20 32  37 20 6f 75 74 20 6f 66  |nt pin 27 out of|
00000af0  20 74 68 65 20 77 61 79  20 6f 66 20 74 68 65 20  | the way of the |
00000b00  73 6d 61 6c 6c 20 77 69  72 65 20 79 6f 75 20 6a  |small wire you j|
00000b10  75 73 74 20 73 6f 6c 64  65 72 65 64 20 6f 6e 20  |ust soldered on |
00000b20  20 0d 61 74 74 61 63 68  20 74 68 69 73 20 74 6f  | .attach this to|
00000b30  20 74 68 65 20 63 65 6e  74 72 65 20 70 6f 6c 65  | the centre pole|
00000b40  20 6f 66 20 74 68 65 20  73 77 69 74 63 68 2e 54  | of the switch.T|
00000b50  68 65 20 6f 74 68 65 72  20 74 77 20 6f 20 74 65  |he other tw o te|
00000b60  72 6d 69 6e 61 6c 73 20  6f 66 20 20 0d 74 68 65  |rminals of  .the|
00000b70  20 73 77 69 74 63 68 20  67 6f 20 74 6f 20 70 69  | switch go to pi|
00000b80  6e 20 31 34 20 28 47 4e  44 29 20 61 6e 64 20 32  |n 14 (GND) and 2|
00000b90  38 20 28 56 43 43 29 2e  20 20 0d 36 2e 50 69 6e  |8 (VCC).  .6.Pin|
00000ba0  20 32 38 20 61 6c 73 6f  20 6d 75 73 74 20 62 65  | 28 also must be|
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00000ff0  0d                                                |.|
00000ff1