how to buffer serial data on pic?

[kiteman]

Hi Languer,
do you have some sample of program to write byte byte on the follow memory by SPI? I ordered 23A256 (2 bank)
I receive data at 57600 I have about 170 us of time to write data in memory
thankyou

SRAM Options
Microchip maxes out at 32 Kbytes, so you could try two of these (23A256 or 23K256). You would have to "bank select" between the two ICs using the CS lines.

OnSemi also seems to max out at 32 Kbytes (N25S830HAS22I).

You would most likely operate both these options in "Sequential/Burst Mode".

FRAM Options
RAMTRON has the FM25V05 which would allow 64 Kbytes. These do have a limit on the amount of write operations (since they do retain data after power is lost), although it is quite high.

[languer]

This is by no means complete code, but a starting point would be something like shown below...

The SERIN/SEROUT are defined by you application.

getData:
	'[SRAM BANK 0]

	'BANK SELECT
	SRAM1_CS = 0                'SRAM CHIP #1 ENABLED
	SRAM2_CS = 1                'SRAM CHIP #2 DISABLED

	'BANK WRITE ADDRESS
	spi_data = WRITE_INSTR
	WriteSPI
	tx_spi_data = addr.HIGHBYTE
	WriteSPI
	tx_spi_data = addr.LOWHBYTE
	WriteSPI

	'GET SERIN INTO FIRST BANK
	For i = 0 to DATA_LENGTH
		SERIN tx_spi_data
		WriteSPI
	Next i

	'[SRAM BANK 1]

	'BANK SELECT
	SRAM1_CS = 1                'SRAM CHIP #2 DISABLED
	SRAM2_CS = 0                'SRAM CHIP #1 ENABLED

	'BANK WRITE ADDRESS
	tx_spi_data = WRITE_INST
	WriteSPI
	tx_spi_data = addr.HIGHBYTE
	WriteSPI
	tx_spi_data = addr.LOWHBYTE
	WriteSPI

	'GET SERIN INTO SECOND BANK
	For i = 0 to DATA_LENGTH
		SERIN tx_spi_data
		WriteSPI
	Next i


sendData:
	'[SRAM BANK 0]

	'BANK SELECT
	SRAM1_CS = 0                'SRAM CHIP #1 ENABLED
	SRAM2_CS = 1                'SRAM CHIP #2 DISABLED

	'BANK WRITE ADDRESS
	spi_data = WRITE_INSTR
	WriteSPI
	tx_spi_data = addr.HIGHBYTE
	WriteSPI
	tx_spi_data = addr.LOWHBYTE
	WriteSPI

	'SEND SEROUT FROM FIRST BANK
	For i = 0 to DATA_LENGTH
		ReadSPI
		SEROUT rx_spi_data
	Next i

	'[SRAM BANK 1]

	'BANK SELECT
	SRAM1_CS = 1                'SRAM CHIP #2 DISABLED
	SRAM2_CS = 0                'SRAM CHIP #1 ENABLED

	'BANK WRITE ADDRESS
	spi_data = WRITE_INSTR
	WriteSPI
	tx_spi_data = addr.HIGHBYTE
	WriteSPI
	tx_spi_data = addr.LOWHBYTE
	WriteSPI
								                                  
	'SEND SEROUT FROM SECOND BANK
	For i = 0 to DATA_LENGTH
		ReadSPI
		SEROUT rx_spi_data
	Next i

Necessary defines (copied from PRSTEIN's code - http://www.picbasic.co.uk/forum/showthread.php?t=12766):

' Definations for the SPI communication protocal 
'------------------------------------------------------------------
SRAM1_CS        VAR PORTC.0  ' SPI SRAM CHIP #1 CS PIN
SRAM1_CS_TRIS   VAR TRISC.0  ' SPI SRAM CHIP #1 CS PIN DIRECTION
SRAM2_CS        VAR PORTC.1  ' SPI SRAM CHIP #2 CS PIN
SRAM2_CS_TRIS   VAR TRISC.1  ' SPI SRAM CHIP #2 CS PIN DIRECTION

SCK            VAR PORTC.3  ' SPI CLOCK
SCK_TRIS       VAR TRISC.3  ' SPI CLOCK PIN DIRECTION CONTROL
SDI            VAR PORTC.4  ' SPI DATA IN
SDI_TRIS       VAR TRISC.4  ' SPI DATA IN PIN DIRECTION 
SDO            VAR PORTC.5  ' SPI DATA OUT PIN
SDO_TRIS       VAR TRISC.5  ' SPI DATA OUT PIN

WCOL           VAR SSPCON.7 'SSP WRITE COLLISION
SSPEN          VAR SSPCON.5 'SSP ENABLE
SSPIF          VAR PIR1.3   'SSP INTERRUPT FLAG
'---------------------------------------------------------------------

'-------------SPI PORT REGISTERS SETUP----------------------------------------
SSPSTAT = %01000000         ' SAMPLE AT THE MIDDLE OF DATA OUTPUT TIME, TRANSMIT ON IDLE RISING EDGE OF SCK
SSPCON = %00100000          ' SPI MASTER MODE, CLOCK=Fosc/4  ENABLE HARDWARE SPI PORT
SSPEN = 1                   ' ENABLE HARDWARE SPI PORT
'-------------------------------------------------------------------------------

'-------------INITIALIZATION--------------------------------------------------
SRAM1_CS = 1                'SRAM CHIP #1 DISABLED
SRAM2_CS = 1                'SRAM CHIP #2 DISABLED
SRAM1_CS_TRIS = 0           'OUTPUT 
SRAM2_CS_TRIS = 0           'OUTPUT 
SDO = 1                     'START SPI PIN WITH HIGH
SDO_TRIS = 0                'OUTPUT 
SDI_TRIS = 1                'INPUT 


'-------------VARIABLES---------------------------------------------------------
i VAR WORD
addr VAR WORD
tx_spi_data VAR BYTE
rx_spi_data VAR BYTE
DATA_LENGTH CON 30716
'-------------------------------------------------------------------------------

The WriteSPI and ReadSPI functions below can be GOSUBs, or INLINED (i.e. pasted directly where the functions appear) for faster performance.

WriteSPI:
	SSPIF = 0                 'CLEAR INTERRUP FLAG
	WCOL = 0                  'CLEAR COLLISION BIT BEFORE WRITING TO SPI
	SSPBUF = tx_spi_data      'SEND BYTE
	WHILE(!SSPIF)             'WAIT FOR BYTE TO BE CLOCKED-OUT/CLOCKED-IN - THIS HAPPENS SIMULTANEOUSLY
	WEND
	rx_spi_data = SSPBUF      'STORE RECEIVED DATA
	SSPIF = 0                 'CLEAR INTERRUP FLAG
RETURN

ReadSPI:
	SSPIF = 0                 'CLEAR INTERRUP FLAG
	WCOL = 0                  'CLEAR COLLISION BIT BEFORE WRITING TO SPI
	SSPBUF = 0                'SEND/CLOCK-OUT DUMMY BYTE TO CLOCK-IN RECEIVED BYTE
	WHILE(!SSPIF)             'WAIT FOR 8-BITS TO BE CLOCKED-OUT/CLOCKED-IN - THIS HAPPENS SIMULTANEOUSLY
	WEND
	rx_spi_data = SSPBUF      'STORE RECEIVED DATA
	SSPIF = 0                 'CLEAR INTERRUP FLAG
RETURN

Note that there is quite a bit of optimization possible. In the places where you will be accessing the RS232 port right after the SPI commands; you could remove the wait states on the SPI commands (i.e. WHILE-WEND). All you need to make sure is that you allow sufficient time for the 8-bits to clock out; which the RS232 processing takes care of.

Also note that during this whole process you are buffering data into SRAM (or out of SRAM) sequentially (e.g. you receive an RS232 byte and store it, and again). This means that if you have qualifiers required to be read (or transmitted) at the beginning or end of your packet, then you have to handle this separately (e.g. receive-process-validate first, then enter the buffering routine).