retlw   error           ;RDY status was not present in the alloted
				;time, return with error status.
rdynoerr
IF      wire3
;setup RA1 back to output
	movlw   0               ;set porta as output
	tris    serial          ;      / 
ENDIF
	retlw   no_err

;********************************************************************
;*                      SEE                                         *
;********************************************************************

				;See will control the entire operation of a
				;93CX6 device.  Prior to calling the routine,
				;load a valid command/memory address into
				;location cmd, and for WRITE or WRAL
				;commands, load registers highb and lowb with
				;16 bits of write data.  Upon exit, the W
				;register will contain the completion status.
				;Only 93CX6 instructions which require a
				;status check can return with an error as the
				;completion status.  The values that denote
				;the completion status are defined as
				;variables 'error' and 'no_err' in the
				;general assignments section.

see     
	movf    cmd,w           ;save cmd
	movwf   temp_cmd
	movf    addr,w          ;save addr
	movwf   temp_addr       ;
	movlw   cmd             ;Load W with the location of the cmd
				;register.
	movwf   fsr             ;Transfer that information into the File
				;Select Register.  The fsr now points to
				;location cmd.
	sel                     ;Select the 93CX6.
	strtbt                  ;Send a start bit.
;
	btfsc   cmd,7           ;bit 7 = 0?
IF      XC46
	goto    sca8            ;xfer 8 bit cmd/adr
ENDIF
IF      LC468
	goto    sca9            ;xfer 9 bit cmd/adr
ENDIF
IF      H16     
	goto    sca10           ;xfer 10 bit cmd/adr
ENDIF
IF      H8
	goto    sca11           ;xfer 11 bit cmd/adr
ENDIF

;        goto    set_cmd_addr    ;no then set cmd/addr
	btfss   cmd,6           ;bit 6 = 0 ?   
IF      XC46
	goto    sc8             ;xfer 8 bit cmd/adr
ENDIF
IF      LC468
	goto    sc9             ;xfer 9 bit cmd/adr
ENDIF   
IF      H16     
	goto    sc10            ;xfer 10 bit cmd/adr
ENDIF
IF      H8
	goto    sc11            ;xfer 11 bit cmd/adr
ENDIF
;        goto    set_cmd         ;yes then set cmd
IF      XC46
	goto    sca8            ;xfer 8 bit cmd/adr
ENDIF
IF      LC468
	goto    sca9            ;xfer 9 bit cmd/adr
ENDIF
IF      H16     
	goto    sca10           ;xfer 10 bit cmd/adr
ENDIF
IF      H8
	goto    sca11           ;xfer 11 bit cmd/adr
ENDIF

;        goto    set_cmd_addr    ;else set cmd/addr
see1
	movf    temp_cmd,w      ;retore cmd     
	movwf   cmd             ;       /
	movf    temp_addr,w     ;restore addr
	movwf   addr            ;       /
	btfsc   cmd,6           ;Check for a WRITE or ERASE command.
	goto    see2            ;Yes, parse the command further.
	btfsc   cmd,7           ;Check for a READ command.
	goto    read_           ;Yes, process READ command.
	btfsc   cmd,5           ;Check for a EWEN or ERAL command.
	goto    see3            ;Yes, parse the command further.
	btfsc   cmd,4           ;Check for a WRAL command.
	goto    write_          ;Yes, process WRITE/WRAL command.

exit_   dsel                    ;No further processing required; 93CX6
				;command completed.
;
	retlw   no_err          ;Return with good completion status.

see2    btfss   cmd,7           ;Check for a ERASE command.
	goto    write_          ;No, process WRITE command.
exit2_  call    rdychk          ;ERASE command requires a status check.
	dsel                    ;De-select the 93CX6.
	addwf   pc              ;Compute completion status from results of
				;status check.
	retlw   no_err          ;Return with good completion status.
	retlw   error           ;Return with bad completion status.

see3    btfsc   cmd,4           ;Check for a EWEN command.
	goto    exit_           ;Yes, no further processing required, exit
				;now.
	goto    exit2_          ;No, ERAL command which requires a status
				;check.

read_   incf    fsr             ;Increment the File Select Register to point
				;to the register receiving the upper byte of
				;the incomming 93CX6 data word.
	call    din8            ;Input the upper byte.
IF      org8
ELSE
	incf    fsr             ;Increment the File Select Register to point
				;to the register receiving the lower byte.
	call    din8            ;Input 8 more bits.
ENDIF
	goto    exit_           ;No further processing required, exit now.

write_  incf    fsr             ;Increment the File Select Register to point
				;to the upper byte of the 16 bit 93CX6 data
				;word to be transmitted.
	call    dout8           ;Output that byte.
IF      org8
ELSE
	incf    fsr            ;Increment the File Select Register to point
			       ;to the lower byte.
	call    dout8          ;Output the lower byte of the 16 bit 93CX6
			       ;data word.
ENDIF
	goto    exit2_          ;Exit with a status check.

;
;
IF      XC46
sca8
	movlw   b'11000000'     ;clr all but hi 2
	andwf   cmd,w           ;save in w
	iorwf   addr            ;mask in addr.
	incf    fsr             ;inc FSR
	call    dout8           ;output
	goto    see1            ;return
ENDIF
IF      LC468
;
sca9
	bcf     addr,7          ;clr hi of addr
	btfsc   cmd,6           ;xfer cmd's bit 6
	bsf     addr,7          ;to addr's bit 7
	call    dout9           ;output
	goto    see1            ;return
ENDIF
IF      H16
;
sca10   
	call    dout10          ;output cmd reg
	goto    see1            ;return
ENDIF                
;
IF      H8
sca11
	bcf     cmd,5           ;xfer cmd's bit 3 to
	btfsc   cmd,3           ;cmd's bit 5
	bsf     cmd,5           ;       /
	call    dout11          ;output
	goto    see1            ;return
;
ENDIF
;
;
;
IF      XC46
sc8
	movf    cmd,w           ;get command
	movwf   addr            ;save in addr
	incf    fsr             ;inc pointer
	call    dout8           ;output
	goto    see1            ;return
;
ENDIF
IF      LC468
sc9     
	rlf     cmd,w           ;rotate cmd left
	movwf   addr            ;save in addr
	call    dout9           ;xfer 9 bits
	goto    see1            ;return
ENDIF
IF      H16
;
sc10    
	rlf     cmd             ;rotate cmd
	rlf     cmd,w           ;left twice
	movwf   addr            ;save in addr
	clrf    cmd             ;clear command
	call    dout10          ;xfer 10 bits
	goto    see1            ;return
ENDIF
;
IF      H8
sc11
	bcf     addr,7          ;xfer cmd's bit 4
	btfsc   cmd,4           ;to addr's bit 7
	bsf     addr,7          ;       /
	call    dout11          ;xfer 11 bits
	goto    see1            ;return
ENDIF
;********************************************************************
;*                      Test Program                                *
;********************************************************************
	main                    ;We've include a sample program to exercise
				;the PIC to 93C66 interface using a simple
				;erase, write and verify routine.
				;8 bit organization has been used
				;with a 3 wire interface.
	
	clrf    serial          ;Clear the port tied to the 93C66 device.
	movlw   b'11110000'     ;Intialize the data direction register for
	tris    serial          ;that port.
	
	movlw   ewen            ;Load W with the Erase/Write Enable command.
	movwf   cmd             ;Transfer W into cmd register.
	call    see             ;Enable the 93C66 device.

	movlw   eral            ;Load W with the Erase All command.
	movwf   cmd             ;Transfer W into cmd register.
	call    see             ;Erase the 93C66.
	xorlw   error           ;Check completion status.
	btfsc   status, zflag   ;Test for error condition.
	goto    errloop         ;Yes, bad completion status, error-out.

				;Write loop:
tstptrn equ     0xAA            ;Define the test pattern to be written.

	movlw   write           ;Load W with the Write command.
	movwf   cmd             ;Transfer W into cmd register.
	movlw   tstptrn         ;Intialize the 93C66 data registers with
				;write data.
	movwf   highb           ;load in high byte only
				;since 8 bit low byte is ignored
	clrf    addr            ;start at addr 0
test1   call    see             ;Write data word into 93C66 device.
	xorlw   error           ;Check completion status.
	btfsc   status,zflag    ;Test for error condition.
	goto    errloop         ;Yes, bad completion status, error-out.
	incfsz  addr            ;No, increment the 8 bit memory address
				;field.
	goto    test1           ;write another location
	btfss   cmd,3           ;see if all done
	goto    wrt_nxt_pg      ;no then write next page
	goto    read_tst        ;read written data
wrt_nxt_pg
	bsf     cmd,3           ;set page bit
	goto    test1           ;No, write another location.

				;Read loop:
read_tst
	movlw   read            ;Load W with the Read command.
	movwf   cmd             ;Transfer W into cmd register.
test2   call    see             ;Read addressed data word from 93C66 device.
	movlw   tstptrn         ;Load W with the pattern written.
	subwf   highb,w         ;Verify the data read against what was
				;written.
	btfss   status,zflag    ;Same?
	goto    errloop         ;No, error-out.
	incfsz  addr            ;Yes, both byte correct, increment the 8 bit
				;memory address field.
	goto    test2           ;do next byte
	btfss   cmd,3           ;check page bit
	goto    rd_nxt_pg       ;no then chk next page
	goto    allok           ;all done!!!
rd_nxt_pg
	bsf     cmd,3           ;set page bit
	goto    test2           ;No, read another location.

allok   goto    allok           ;Home safe!
;
;
errloop
	goto    errloop
;
;
;
;KEY DEFINITIONS
;
	ORG     PIC54
SYS_RESET
	GOTO    START
;
	END