TITLE        "R/W EEPROM"
LIST  P = 16C54
;Serial Eprom interface to PIC16C5X.
;REV 2.0        8/26/92.
;
;Define Equates:
;       
	PIC54   EQU     1FFH
;
PAGE
;
	ORG     0
START
	goto    main            ;run test program
;
PAGE
;
TRUE    EQU     1
FALSE   EQU     0
S93C46  EQU     FALSE
S93LC46 EQU     FALSE
S93C56  EQU     FALSE
S93LC56 EQU     FALSE
S93C66  EQU     TRUE
S93LC66 EQU     FALSE
wire3   equ     TRUE
org8    EQU     FALSE
;
IF      S93LC46
	IF      org8
	LC468   EQU     TRUE
	XC46    EQU     FALSE
	H16     EQU     FALSE
	H8      EQU     FALSE
	ELSE
	LC468   EQU     FALSE
	XC46    EQU     TRUE
	H16     EQU     FALSE
	H8      EQU     FALSE
	ENDIF
ELSE
ENDIF
IF      S93C46
	LC468   EQU     FALSE
	XC46    EQU     TRUE
	H16     EQU     FALSE
	H8      EQU     FALSE
ENDIF
IF      S93C56 + S93C66 + S93LC56 + S93LC66
	IF      org8
	H8      EQU     TRUE
	H16     EQU     FALSE
	LC468   EQU     FALSE
	XC46    EQU     FALSE
	ELSE
	H16     EQU     TRUE
	H8      EQU     FALSE
	LC468   EQU     FALSE
	XC46    EQU     FALSE
	ENDIF
ELSE
ENDIF



;********************************************************************
;*                      Register Assignments                        *
;********************************************************************

indir   equ     0       ;Use this register as source/destination
			;for indirect addressing.
pc      equ     2       ;PIC Program Counter.
status  equ     3       ;PIC Status Register.
fsr     equ     4       ;File Select Register.
serial  equ     5       ;Port used for 93CX6 control. 
			;The following four registers must be
			;located consecutively in memory.
cmd     equ     1a      ;This register contains the 4 bit
			;command op code for 93CX6 as follows:
			;bit 7 msb of command op code
			;bit 6 next bit of op code
			;bit 5 next bit of op code
			;bit 4 lsb of op code
			;bit 3 A8 of address in case of
			;56/66 in 8 bit mode.
addr    equ     1b      ;memory address of lower 7/8 bits
highb   equ     1c      ;Used in read/write routines to store the
			;upper byte of a 16 bit data word,
			;or the data in a 8 bit data word
lowb    equ     1d      ;Used in read/write routines to store the
			;lower byte of a 16 bit data word,
			;or not used in 8 bit data word.

cnthi   equ     1e      ;Used as the upper byte of a sixteen bit
			;loop counter in RDYCHK routine.
cnt     equ     1f      ;Used as the lower byte of a sixteen bit 
			;loop counter in RDYCHK routine, and 
			;elswhere as an eight bit counter.
temp_cmd equ    1e      ;doubles as a temp register for cmd        
temp_addr equ   1f      ;doubles as a temp register for addr

;********************************************************************
;*                      Bit Assignments                             *
;********************************************************************

carry   equ     0               ;Carry Flag of Status Register.
zflag   equ     2               ;Zero Flag of Status Register.

cs      equ     2               ;Port pin tied to CS on 93CX6.
din     equ     1               ;Port pin tied to DI on 93CX6.
dout    equ     1               ;Port pin tied to DO on 93CX6.
clock   equ     3               ;Port pin tied to CLK on 93CX6.

;********************************************************************
;*                      General Assignments                         *
;********************************************************************

no_err  equ     0               
error   equ     1               
tries   equ     20      ;After issuing a WRITE, ERASE, ERAL, or WRAL
			;command, the approximate number of machine
			;cycles X 256 to wait for the RDY status.
			;This value must be adjusted for operating
			;frequencies other than 4 MHz.

read    equ     b'10000000'     ;read command op code
write   equ     b'01000000'     ;write command op code
erase   equ     b'11000000'     ;erase command op code
ewen    equ     b'00110000'     ;erase enable command op code
ewds    equ     b'00000000'     ;erase disable command op code
eral    equ     b'00100000'     ;erase all command op code
wral    equ     b'00010000'     ;write all command op code

;********************************************************************
;*                      Macro Definitions                           *
;********************************************************************

sel     MACRO                   ;Selects the 93CX6 device.
	bsf     serial,cs       ;Chip Select (CS) = '1' to select
	ENDM                    ;the device                

dsel    MACRO                   ;De-select the 93CX6 device.
	bcf     serial,cs       ;Chip Select (CS) = '0' to de-select
				;the device.
	ENDM

strtbt  MACRO                   ;Issue the Start Bit to the 93CX6.
	bsf     serial,din      ;Start Bit = '1'.
	clkit                   ;Clock it out.
	ENDM

clkit   MACRO                   ;Clocks a serial data bit into or out
				;of the 93CX6 device.
	bsf     serial,clock    ;Clock (CLK) = '1'.

	nop             ;Adjust the number of nop instructions
			;between the assertion and de-assertion of
			;CLK in proportion to the PIC operating
			;frequency.  Refer to the 93CX6 data for the
			;minimum CLK period.
				
	bcf     serial,clock    ;Clock (CLK) = '0'.
	ENDM
;
PAGE
;********************************************************************
;*                      DOUTx                                       *
;********************************************************************
;doutxx, outputs up to 11 bits of op code/data, depending on whether
;a 46/56/66 serial eeprom is being used. The number of bits over 8 are
;saved in the cmd register and the rest in the addr register. Before
;calling this routine the cmd and the addr registers should be loaded
;as follows:
;cmd reg.bits 7|6|5|4|3|2|1|0
;--------------|-|-|-|-|-|-|-|
;             X|X|X|X|X|X|X|Y| --> not used
;             X|X|X|X|X|X|Y|X| --> mot used
;             X|X|X|X|X|Y|X|X| --> not used
;             X|X|X|X|Y|X|X|X| --> 9th bit of address if necessary
;             X|X|X|Y|X|X|X|X| --> lsb of command op code
;             X|X|Y|X|X|X|X|X| --> 3rd bit of command op code
;             X|Y|X|X|X|X|X|X| --> 2nd bit of command op code
;             Y|X|X|X|X|X|X|X| --> msb of command op code
;
;addr reg. 6/7/8 bits of address if necessary.

IF      H8
dout11
	bcf     serial,din
	rlf     indir           ;rotate thru carry
	btfsc   status,carry    ;set?        
	bsf     serial,din      ;yes, set output to 1
	clkit                   ;clk data
ENDIF
IF      H16+H8
dout10
	rlf     indir           ;rotate thru carry
	bcf     serial,din      ;set output to 0
	btfsc   status,carry    ;set?
	bsf     serial,din      ;else set output to 1
	clkit                   ;clk data
ENDIF
IF      H8+H16+LC468
dout9
	rlf     indir           ;rotate thru carry
	bcf     serial,din      ;set output to 0
	btfsc   status,carry    ;set?
	bsf     serial,din      ;else set output to 1
	clkit                   ;clk data
	incf    fsr             ;inc pointer
ENDIF
dout8
	movlw   8               ;Initialize loop counter.
	movwf   cnt             
;
d_o_8   bcf     serial,din      ;Assume that the bit to be transfered is a
				;'0'.  Hence, de-assert DI.
	rlf     indir           ;Rotate the actual bit to be transferred into
				;the carry bit.
	btfsc   status,carry    ;Test the carry, if our assumption was
				;correct, skip the next instruction.
	bsf     serial,din      ;No, actual bit was a '1'.  Assert DI.
	clkit                   ;Clock the 93CX6.
	decfsz  cnt             ;Repeat until cnt = 0.
	goto    d_o_8           ;Cnt still > 0.
	rlf     indir           ;Restore register to its original condition.
	bcf     serial,din      ;make sure din is low        
	retlw   no_err          ;Exit with good status.

;********************************************************************
;*                      DIN8                                        *
;********************************************************************
				;Din8 will input 8 bits of data from the
				;93CX6.  Before calling this routine, the FSR
				;must point to the register being used to
				;hold the incomming data.
din8    
IF      wire3
;set up the RA1 as a input before proceeding        
	movlw   b'00000010'     ;set up porta
	tris    serial          ;
ENDIF
	movlw   8               ;Initialize loop counter.
	movwf   cnt             ;

d_i_8   
	rlf     indir           ;Make room for the incomming bit in the
				;destination register.
	bcf     indir,0         ;Assume that the incomming bit is a '0' and
				;clear the LSB of the destination register.
	clkit                   ;Clock a bit in the 93CX6.
	btfsc   serial,dout     ;Test the incomming bit, if our assumption
				;was correct, skip the next instruction.
	bsf     indir,0         ;No, actual bit is a '1'.  Set the LSB of the
				;destination register.
	decfsz  cnt             ;Repeat until cnt = 0.
	goto    d_i_8           ;Cnt still > 0.
IF      wire3
;setup RA1 back to output
	movlw   0               ;set RA1 as output
	tris    serial          ;      / 
ENDIF
	retlw   no_err          ;Exit with good status.

;********************************************************************
;*                      RDYCHK                                      *
;********************************************************************
				;Rdychk will read the 93CX6 READY/BUSY status
				;and wait for RDY status within the alloted
				;number of processor cycles.  If RDY status
				;is not present after this set period, the
				;routine will return with an error status.

rdychk  
IF      wire3
;set up RA1 as a input before proceeding        
	movlw   b'00000010'     ;set up porta
	tris    serial          ;
ENDIF
	movlw   tries           ;Initialize time-out counter.
	movwf   cnthi           ;
	clrf    cnt             ;
	dsel                    ;De-select the 93CX6.

;       nop                     ;NOTE:  Check the 93CX6 data sheet for
				;minimum CS low time.  Depending upon
				;processor frequency, a nop(s) may be
				;between the assertion and de-assertion of
				;Chip Select.

	sel                     ;Re-select the 93CX6.
notrdy  btfsc   serial,dout     ;If DO is a '0', 93CX6 has yet to completed
				;the last operation (still busy).
	goto    rdynoerr        ;skip to no error
	decfsz  cnt             ;No, not yet ready.  Decrement the LSB of our
				;16 bit timer and check for expiration.
	goto    notrdy          ;Still some time left.  Try again.
	decfsz  cnthi           ;Least significant byte expired - decrement
				;and check for expiration of the MSB.
	goto    notrdy          ;Still some time left.  Try again.
IF      wire3
;setup RA1 back to output
	movlw   0               ;set RA1 as output
	tris    serial          ;      / 
ENDIF