SRAM
(Static RAM) OR EEPROM READER/WRITER
I have been interested on eeproms and srams and how to write and read bytes from them. The great diversity of these devices, actual and obsolete made me study and experiment with them as all hobbists will say “there’s no experience like hands on experience” or “seeing (verifiying) is believing”.
SRAMS
and EEPROMS are very alike in the way you acess them. A memory address is selected using the addres bus. There are signals that are use to enable
the chip, enable write, enable read (output enable) and strobe
that must be set high or low depending if it is a write or a read
cycle. Then the data is read or written
on the data bus.
SRAMS
can be written an almost infinite number of times, EEPROMS have a limit more
shorter like 1000, or 100,000 (of my
actual knowledge) write cycles.
The
device I built can be used for:
-Program
EEPROMS for microcontroller boards
-Read
EEPROMS and dump them to a file on your PC (like from games cartridges).
-Copy a
ROM, EPROM to a modern device (EEPROM)
-Program
SRAMS with a lithium battery instead of EEPROMS during the developing stage of
a microcontroller board (to save money!).
It is
very cheap and uses the parallel port.
The software runs on DOS.
This is
the schematics
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The
LPT base address is 378h (8 output bits).
LPT Status is 378h +1. LPT
Control is 378h + 2. The Data is
read using the 74LS157 in nibble mode.
LPTControls clocks the counter, resets it, selects read/write and selects nibble A/B. |
This is the
first prototype
This is
the board (the big chip is the UMC6116 2k SRAM)
These
are screenshots of the program
Selecting the source file
Reading
the contents of the memory
Write
protect switch (removes power from every circuit except the SRAM)
The
program was written on basic and compiled using TurboBasic 1.0
5 DIM A$(1)
10 LPTData=&H378
20 LPTStatus=LPTData+1
30 LPTControl=LPTData+2
40 CLS
50 INPUT "Read or Write :",op$ :
op$=UCASE$(op$)
60 IF op$="W" THEN GOSUB 100
70 IF op$="R" THEN GOSUB 210
80 IF op$="" THEN END
90 GOTO 40
100 'WRITE SUBROUTINE
110 LINE INPUT "Source Filename: ",filename$
120 OPEN filename$ FOR INPUT AS #1
125 OUT LPTControl,(INP(LPTControl) OR &H08):
'Enable/RST
130 IF EOF(1)<>0 THEN GOTO 205
135 K=K+1
140 A$(1)=INPUT$(1,1)
150 OUT LPTControl,(INP(LPTControl) AND &HFB): '0
for write
160 OUT LPTData,ASC(A$(1))
170 gosub 340
180 GOSUB 280
190 PRINT CHR$(A);
200 GOTO 130
205 CLOSE #1
206 IF K<2048 THEN GOSUB 420
207 OUT LPTControl,(INP(LPTControl) OR &H04): '1
for read NORMAL
208 OUT LPTControl,(INP(LPTControl) AND
&HF7):RETURN
210 'READ SUBROUTINE
215 OUT LPTControl,(INP(LPTControl) OR &H08):
'Enable/RST
220 OUT LPTControl,(INP(LPTControl) OR &H04): '1
for read
230 FOR I=1 to 2048
240 GOSUB 340
250 GOSUB 280
260 PRINT CHR$(A);
270 NEXT I
275 OUT LPTControl,(INP(LPTControl) AND &HF7)
276 PRINT : PRINT "Press any key to
continue."
277 IF INKEY$="" THEN GOTO 277
278 RETURN
280 'Clock Write Count
290 OUT LPTControl,(INP(LPTControl) OR &H02):
'Clock Low
300 FOR J=1 TO 10: NEXT J
310 OUT LPTControl,(INP(LPTControl) AND &HFD):
'Clock High
320 FOR J=1 TO 10: NEXT J
330 RETURN
340 'Read BUS sub
350 OUT LPTControl,(INP(LPTControl) OR &H01)
360 A=(INP(LPTStatus) AND &HF0)/&H10
370 OUT LPTControl,(INP(LPTControl) AND &HFE)
380 A=A OR (INP(LPTStatus) AND &HF0)
390 A=A XOR &H88
400 RETURN
420 FOR I=1 TO 2047-K
430 OUT LPTData,&HFF
440 GOSUB 340
450 GOSUB 280
460 PRINT CHR$(A);
470 NEXT I
480 RETURN
For a 2k byte (2048 bytes) memory, (2^11= 2048) eleven address lines are
neede, that’s way I used the 12 bit binary counter (4040) but for a 4k (4096)
the twelve lines will be used and the program will be modified acordingly. The 4020 CMOS 14 bit binary counter will be
enough for a 16k byte memory. So
depending on the memory size, an apropiate counter must be used.