Next up is an AT24C256
This is a 32KB Non-volatile Memory Module
WARNING: The default ID is &50 which is the SAME device ID as the Minerva Mk2 so MUST be changed
For the purposes of the test programs I enabled jumper A2 which changes the address to &54
The device (with ID still set to &50 which caused all sorts of QL/Minerva problems until changed)
In theory you can have 8 of these devices on the same i2c bus, but because of Minerva's ID you can only have 7
The 32kb is treated as 512 pages x 64 bytes and is addressed with a 15bit address in the commands
So XPPPPPPP PPBBBBBB (where X=Don’t care, P=Page 0 to 511, B=Byte 0 to 63)
Writing can be done as a single byte or up to 64 bytes
Writes are always to a single page and will wrap back to the start of the page if the end is reached (so only the lowest 6 bits of the address are incremented)
Reading can be done as a single byte or multiple bytes either sequentially or randomly (a dummy write is done to move the pointer for random access)
When reading if you don't use a dummy write to put the address pointer where you want it it will use the current position of the internal address pointer. This current address pointer remains over all read/write operations as long as power isn't removed
A simple test of writing and then reading back a single byte
Code: Select all
100 v=123 : REMark byte to write then read
110 a1=0 : REMark msb of address word (bit 8 ignored)
120 a2=0 : REMark lsb of address word
130 REMark Write byte
140 c$=CHR$(164) & CHR$(a1) & CHR$(a2) & CHR$(v) & CHR$(255)
150 r$=I2C_IO(c$,0,HEX('54'),3) : REMark write address + 1 byte
155 PAUSE 15
160 REMark Random access Read Byte (dummy write then read)
170 c$=CHR$(160) & CHR$(a1) & CHR$(a2) & CHR$(255)
180 r$=I2C_IO(c$,0,HEX('54'),2) : REMark position for read
190 c$=CHR$(188) & CHR$(255)
200 r$=I2C_IO(c$,2,HEX('54'),1) : REMark read byte
210 PRINT CODE(r$) & " : ";
220 IF CODE(r$)<>v THEN PRINT "WRONG VALUE READ!!!"
230 IF CODE(r$)=v THEN PRINT "CORRECT VALUE!!!"
A simple test of writing a string (can also be values) then reading back
Code: Select all
100 v$="This is a test of a Page Write (Max 64 Chars)"
110 a1=0 : REMark msb of address word (bit 8 ignored)
120 a2=0 : REMark lsb of address word
130 REMark Write Page
140 c$=CHR$(164) & CHR$(a1) & CHR$(a2) & v$ & CHR$(255)
150 r$=I2C_IO(c$,0,HEX('54'),LEN(v$)) : REMark write address + string/values
155 PAUSE 15
160 REMark Random access Read Byte (dummy write then read)
170 c$=CHR$(160) & CHR$(a1) & CHR$(a2) & CHR$(255)
180 r$=I2C_IO(c$,0,HEX('54'),2) : REMark position for read
190 c$=CHR$(188) & CHR$(255)
200 r$=I2C_IO(c$,LEN(v$),HEX('54'),LEN(v$)) : REMark read string/values
210 r$=r$(1 TO LEN(r$)-1): PRINT r$ & " : "
220 IF r$<>v$ THEN PRINT "WRONG VALUES READ!!!"
230 IF r$=v$ THEN PRINT "CORRECT VALUE!!!"
