Can't read sequential addresses in external EEPROM

[tjkelly]

I am using a PIC18F2420 with a Microchip 25LC1024 128k x 8 EEPROM.
To get my technique down on using the MSSP I wrote the test code below to write data to the first 2 locations in the EEPROM then to read them back.

If I do two separate reads it works but when I keep the CS low to perform a sequential read and clock the next data byte out of the EEPROM I always get FF.

What am I missing here?

'25LC1024 128k x 8 EEPROM
'PIC18F2420

CS Var PORTB.2
dummy_data Var Byte
Data_Byte1 Var Byte
Data_Byte2 Var Byte


DEFINE OSC 32                  	'32 Mhz Osc


Main:
TRISB=%00000000			'Set CS as an output
TRISC=%00010000			'Set SPI data in, data out and clock out		
SSPSTAT = %01000000    		'Sample in middle, TX rising clock edge
SSPCON1 = %00100010 		'No collision/overflow, enable port,idle low,Fosc/64

High CS
Gosub Write_SPI_data
Gosub Read_SPI_data
Gosub Read_SPI_Data_Sequential
End

Write_SPI_Data:
Gosub Write_Enable
Low CS
SSPBUF = %00000010		' Send Opcode for WRITE sequence
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send MSByte of EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send Middle Byte of EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send LSByte of EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000111		' Send data byte
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
High CS

Gosub Write_Enable		' Write Enable Latch is reset after  
			             '  WRITE instruction successfully
                                                   ' executed so re-enable.
Low CS
SSPBUF = %00000010		' Send Opcode for WRITE sequence
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send MSByte of EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send Middle Byte of EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000001		' Send LSByte of next EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00010000		' Send data byte
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
High CS
Return


Read_SPI_Data:			' This works
Low CS
SSPBUF = %00000011		' Send Opcode for READ sequence
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send MSByte of EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send Middle Byte of EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send LSByte of next EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send dummy data byte to clock data out of EEPROM
While SSPSTAT.0 = 0: Wend 	' Wait for completion
Data_Byte1 = SSPBUF		' Get data from address 0. Should be %00000111
                                                   ' and it is.
High CS                                         ' End of first READ sequence

Low CS				' Perform next READ sequence
SSPBUF = %00000011		' Send Opcode for READ sequence
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send MSByte of EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send Middle Byte of EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000001		' Send LSByte of next EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send dummy data byte to clock data
                                                   ' out of EEPROM.
While SSPSTAT.0 = 0: Wend 	' Wait for completion
Data_Byte2 = SSPBUF		' Get data from address 1. Should be
                                                   ' %00010000 and it is.
High CS				' End of second READ sequence
Return

Read_SPI_Data_Sequential:	             ' This doesn't work
Low CS
SSPBUF = %00000011		' Send Opcode for READ sequence
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send MSByte of EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send Middle Byte of EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send LSByte of next EEPROM address
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
SSPBUF = %00000000		' Send dummy data byte to clock next data out of EEPROM
While SSPSTAT.0 = 0: Wend 	' Wait for completion
Data_Byte1 = SSPBUF		' Get data from address 0. Should be
                                                   ' %00000111 and it is.
				' Internal address pointer is
                                                   ' automatically incremented
SSPBUF = %00000000		' Send dummy data byte to clock data
                                                   ' out of EEPROM.
While SSPSTAT.0 = 0: Wend 	' Wait for completion
Data_Byte2 = SSPBUF		' Get data from address 1. Should be
                                                   ' %00010000 but is %11111111
High CS				' End of READ sequence
Return

Write_Enable:
'Set the write enable latch (enable write operations)
Low CS
SSPBUF = %00000110		' Send Opcode for WREN
While SSPSTAT.0 = 0: Wend 	' Wait for completion
dummy_data = SSPBUF
High CS
Return