working with external memory

[BrianT]

Hi Ruben,

Try this. I have several methods for reading and writing to the M25Pxxx family. All work but the ones not commented out are the fastest. In some infrequent calls I have left the slow routines in place as they don't add any significan time to the download of data from the M25Pxxx memory.

[code]
ReadFromM25P128:
memclk = 0 'data change point
memclk = 1 : reply.7 = memq : memclk = 0
memclk = 1 : reply.6 = memq : memclk = 0
memclk = 1 : reply.5 = memq : memclk = 0
memclk = 1 : reply.4 = memq : memclk = 0
memclk = 1 : reply.3 = memq : memclk = 0
memclk = 1 : reply.2 = memq : memclk = 0
memclk = 1 : reply.1 = memq : memclk = 0
memclk = 1 : reply.0 = memq : memclk = 0
'takes 50 uSecs per character
debug #reply, ", " 'Debug takes 6.7 mSecs
return


RDSRWIP: 'reads the Status Register - waits for WIP bit to go low
'Data from M25P128 changes on fall of clock so sample on rise of clock.
code = $05 'Read Status Register code
gosub sendcode
WIPclr:
for shift = 7 to 0 step -1 'read 8 bit reply
high memclk : reply.0[shift] = memq : low memclk : pauseus 1
next shift
if reply.0 = 1 then wipclr
return

SendCode: 'Serial MSB first sends the CODE byte from PIC to M25P128
TRISE.0 = 0 : PortE.0 = 0 : memclk = 0 'MemClk
TRISC.0 = 0 : PortC.0 = 0 : memd = 0 'MemD
' for shift = 7 to 0 step -1 'send MSB first
' memclk = 0 : memd = code.0[shift] : memclk = 1: pauseus 1 : memclk = 0
' next shift 'this is SLOW ~500 uSecs per character
memclk = 0
memclk = 0 : memd = code.7 : memclk = 1
memclk = 0 : memd = code.6 : memclk = 1
memclk = 0 : memd = code.5 : memclk = 1
memclk = 0 : memd = code.4 : memclk = 1
memclk = 0 : memd = code.3 : memclk = 1
memclk = 0 : memd = code.2 : memclk = 1
memclk = 0 : memd = code.1 : memclk = 1
memclk = 0 : memd = code.0 : memclk = 1
' much faster, takes about 52 uSecs per character
return
/[code]

You can see here I have several methods for reading from the M25P128. The decrementing loop "... for shift = 7 to 0 step -1..." works and is simple BUT it takes about 500 uSecs per character.

HTH
BrianT

[Ruben Pena]

Brian:
Thanks for your fast response...
I am reading wav files stored in the M25P, and using this to send the address:
cs1 = 0 'SEND COMMAND AND ADDRESS
SHIFTOUT MOSI,SCK,1,[$03\8] 'read command $03
SHIFTOUT MOSI,SCK,1 ,[PAGE.BYTE1\8,PAGE.BYTE0\8,00\7]'addr 000000
I send the command and then the 24 bits address,but note in the last address byte I send
only 7 bytes. then I go to a loop to read the data and send it to the port to convert to
analog with a R2R network,until I find a special end of file char to stop the reading.
If I send the 8 bits, I get shifted data. With 7 bits I got the correct data and I can identify
the end of file byte. I do not know why.
the read routine is this:
ASM
MOVLW 8
MOVWF _CNT
SIGUE
BTFSS _MISO ;MOV BIT TO CHR,0
BCF _CHR,0
BTFSC _MISO
BSF _CHR,0
BSF _SCK ;READ AFTER SENDING THE CLOCK
RLF _CHR,1
BCF _SCK
NOP
NOP
NOP
NOP
NOP
DECFSZ _CNT,1
GOTO SIGUE
ENDASM

Am I missing some previous command to set up the chip for reading..?

I will test your routines to see if I got an improvement.
Thanks again...
Ruben de la Pena V.

[Ruben Pena]

Brian:
I only use the read routines for a little wav player. I use a 16F1826 at 16 mhz.(Internal Osc).
The working routines:
'************************************************* *****
TESTREAD:
CS1 = 1
PAUSEUS 200
CS1= 0
code = 03 'read command
gosub sendbyte
code = 0 'higher add.
gosub sendbyte
code = 00 'high add.
gosub sendbyte
code = 0 'low add.
gosub sendbyte
nextread:
GOSUB READBYTE
SEROUT2 LED,32,[HEX2 REPLY," "]
'PORTB = REPLY
PAUSEUS 50
GOTO nextread

sendbyte:
sclk = 0
sclk = 0 : memd = code.7 : sclk = 1
sclk = 0 : memd = code.6 : sclk = 1
sclk = 0 : memd = code.5 : sclk = 1
sclk = 0 : memd = code.4 : sclk = 1
sclk = 0 : memd = code.3 : sclk = 1
sclk = 0 : memd = code.2 : sclk = 1
sclk = 0 : memd = code.1 : sclk = 1
sclk = 0 : memd = code.0 : sclk = 1
return
Readbyte:
sclk = 0 'data change point
sclk = 1 : reply.7 = memq : sclk = 0
sclk = 1 : reply.6 = memq : sclk = 0
sclk = 1 : reply.5 = memq : sclk = 0
sclk = 1 : reply.4 = memq : sclk = 0
sclk = 1 : reply.3 = memq : sclk = 0
sclk = 1 : reply.2 = memq : sclk = 0
sclk = 1 : reply.1 = memq : sclk = 0
sclk = 1 : reply.0 = memq : sclk = 0
return
'*********************************************
I conected the M25P in port A and send the data to the PortB.
It works up to 48 Mhz(audio), but I am using it at 16 KHZ.
The M25P does not need anything aditional to work...
Greetings and thanks again...
Ruben de la Pena V.