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

indir?? equ???? 0x00??????????? ;Use this register as source/destination for
??? ;indirect addressing.
pc????? equ???? 0x02??????????? ;PIC Program Counter.
status? equ???? 0x03??????????? ;PIC Status Register.
fsr???? equ???? 0x04??????????? ;File Select Register.
serial? equ???? 0x05??????????? ;Port used for 93C46 control.? Since Port A
??? ;is 4 bits wide, we'll use all of Port A.

??? ;The following three registers must be
??? ;located consecutively in memory.
cmd???? equ???? 0x10??????????? ;This register contains the 2 bit 93C46
??? ;command is the upper 2 bit positions and
??? ;memory address in the lower 6.
highb?? equ???? 0x11??????????? ;Used in read/write routines to store the
??? ;upper byte of a 16 bit 93C46 data word.
lowb??? equ???? 0x12??????????? ;Used in read/write routines to store the
??? ;lower byte of a 16 bit 93C46 data word.

cnthi?? equ???? 0x13??????????? ;Used as the upper byte of a sixteen bit loop
??? ;counter in RDYCHK routine.
cnt???? equ???? 0x14??????????? ;Used as the lower byte of a sixteen bit loop
??? ;counter in RDYCHK routine, and elsewhere as
??? ;an eight bit counter.

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

carry?? equ???? 0?????????????? ;Carry Flag of Status Register.
***lag?? equ???? 2?????????????? ;Zero Flag of Status Register.

;For the 3 wire interface, connect the din and dout to the same
;i/o line of the PIC16C5X.
cs????? equ???? 0?????????????? ;Port pin tied to CS on 93C46.
din???? equ???? 1?????????????? ;Port pin tied to DI on 93C46.
dout??? equ???? 1?????????????? ;Port pin tied to DO on 93C46.
clock?? equ???? 2?????????????? ;Port pin tied to CLK on 93C46.

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

no_err? equ???? 0?????????????? ;
error?? equ???? 1?????????????? ;
tries?? equ???? 0x04??????????? ;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???? 0x80??????????? ;93C46 Read command.
write?? equ???? 0x40??????????? ;93C46 Write command.
erase?? equ???? 0xC0??????????? ;93C46 Erase command.
ewen??? equ???? 0x30??????????? ;93C46 Erase/Write Enable command.
ewds??? equ???? 0x00??????????? ;93C46 Erase/Write Disable command.
eral??? equ???? 0x20??????????? ;92CXX Erase All command.
wral??? equ???? 0x10??????????? ;92CXX Write All command.

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

sel???? MACRO?????????????????? ;Selects the 93C46 device.
?bsf???? serial,cs?????? ;Chip Select (CS) = '1' to select the device.
?ENDM

dsel??? MACRO?????????????????? ;De-select the 93C46 device.
?bcf???? serial,cs?????? ;Chip Select (CS) = '0' to de-select the
??? ;device.
?ENDM

strtbt? MACRO?????????????????? ;Issue the Start Bit to the 93C46.
?bsf???? serial,din????? ;Start Bit = '1'.
?clkit?????????????????? ;Clock it out.
?ENDM

clkit?? MACRO?????????????????? ;Clocks a serial data bit into or out of the
??? ;93C46 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 93C46 data for the
??? ;minimum CLK period.
???
?bcf???? serial,clock??? ;Clock (CLK) = '0'.
?ENDM

;********************************************************************
;*????????????????????? Power-On/Reset Entry Point????????????????? *
;********************************************************************

reset_? org???? 0x1FF
?goto??? main

;********************************************************************
;*????????????????????? 93C46 Routines????????????????????????????? *
;********************************************************************
?org???? 0x000?????????? ;Locate all subroutines in the lower half of
??? ;a Program Memory Page.

;********************************************************************
;*????????????????????? DOUT8?????????????????????????????????????? *
;********************************************************************
??? ;Dout8 will output 8 bits of data to the
??? ;93C46.? Before calling this routine, the FSR
??? ;must point to the byte being transmitted.

dout8?? movlw?? 0x08??????????? ;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 93C46.
?decfsz? cnt???????????? ;Repeat until cnt = 0.
?goto??? d_o_8?????????? ;Cnt still > 0.
?rlf???? indir?????????? ;Restore register to its original condition.
?retlw?? no_err????????? ;Exit with good status.

;********************************************************************
;*????????????????????? DIN8??????????????????????????????????????? *
;********************************************************************
??? ;Din8 will input 8 bits of data from the
??? ;93C46.? Before calling this routine, the FSR
??? ;must point to the register being used to
??? ;hold the incomming data.
din8??? movlw?? 0x08??????????? ;Initialize loop counter.
?movwf?? cnt???????????? ;
;for the 3 wire interface the direction of the i/o line connected to
;din and dout has to converted from an output to an input.
?movlw?? b'00000010'???? ;convert RA1 to an input
?tris??? serial????????? ;?????? /

d_i_8?? clkit?????????????????? ;Clock a bit out of the 93C46.
?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.
?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
;for a 3 wire interface, convert the RA1 line back to an output
?movlw?? 0?????????????? ;make RA1 to an output
?tris??? serial????????? ;?????? /
?retlw?? no_err????????? ;Exit with good status.

;********************************************************************
;*????????????????????? RDYCHK????????????????????????????????????? *
;********************************************************************
??? ;Rdychk will read the 93C46 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? movlw?? tries?????????? ;Initialize time-out counter.
?movwf?? cnthi?????????? ;
?clrf??? cnt???????????? ;
;for a 3 wire interface, make the RA1 line an input
?movlw?? b'00000010'???? ;
?tris??? serial
?dsel??????????????????? ;De-select the 93C46.

;?????? nop???????????????????? ;NOTE:? Check the 93C46 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 93C46.
notrdy? btfsc?? serial,dout???? ;If DO is a '0', 93C46 has yet to completed
??? ;the last operation (still busy).
?goto??? no_error??????? ;Otherwise RDY status is present within the
??? ;alloted time, and return with good status.
?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.
;for a 3 wire interface, convert RA1 line back to an ouput
?movlw?? 0?????????????? ;convert RA1 to an output
?tris??? serial????????? ;?????? /
?retlw?? error?????????? ;RDY status was not present in the alloted
??? ;time, return with error status.
no_error
;for a 3 wire interface, convert RA1 line back to an ouput
?movlw?? 0?????????????? ;convert RA1 to an output
?tris??? serial????????? ;?????? /
?retlw?? no_err

;********************************************************************
;*????????????????????? SEE???????????????????????????????????????? *
;********************************************************************

??? ;See will control the entire operation of a
??? ;93C46 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 93C46 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???? 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 93C46.
?strtbt????????????????? ;Send a start bit.
?call dout8????????????? ;Transmit the 2 bit command and six bit
??? ;address.
?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; 93C46
??? ;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 93C46.
?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 93C46 data word.
?call??? din8??????????? ;Input the upper byte.
?incf??? fsr???????????? ;Increment the File Select Register to point
??? ;to the register receiving the lower byte.
?call??? din8??????????? ;Input 8 more bits.
?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 93C46 data
??? ;word to be transmitted.
?call??? dout8?????????? ;Output that byte.
?incf??? fsr???????????? ;Increment the File Select Register to point
??? ;to the lower byte.
?call??? dout8?????????? ;Output the lower byte of the 16 bit 93C46
??? ;data word.
?goto??? exit2_????????? ;Exit with a status check.

;********************************************************************
;*????????????????????? Test Program??????????????????????????????? *
;********************************************************************
?main??????????????????? ;We've include a sample program to exercise
??? ;the PIC to 93C46 interface using a simple
??? ;erase, write and varify routine.
?
?clrf??? serial????????? ;Clear the port tied to the 93C46 device.
?movlw?? b'11110100'???? ;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 93C46 device.

?movlw?? eral??????????? ;Load W with the Erase All command.
?movwf?? cmd???????????? ;Transfer W into cmd register.
?call??? see???????????? ;Erase the 93C46.
?xorlw?? error?????????? ;Check completion status.
?btfsc?? status, ***lag?? ;Test for error condition.
?goto??? errloop???????? ;Yes, bad completion status, error-out.

??? ;Write loop:
loopcnt equ???? 0x1F??????????? ;Define an unused location for our test
??? ;program loop counter.
tstptrn equ???? 0xAA??????????? ;Define the test pattern to be written.

?movlw?? .64???????????? ;Initialize that counter.
?movwf?? loopcnt???????? ;
?movlw?? write?????????? ;Load W with the Write command.
?movwf?? cmd???????????? ;Transfer W into cmd register.
?movlw?? tstptrn???????? ;Intialize the 93C46 data registers with
??? ;write data.
?movwf?? highb?????????? ;
?movwf?? lowb??????????? ;
test1?? call??? see???????????? ;Write data word into 93C46 device.
?xorlw?? error?????????? ;Check completion status.
?btfsc?? status,***lag??? ;Test for error condition.
?goto??? errloop???????? ;Yes, bad completion status, error-out.
?incf??? cmd???????????? ;No, increment the 6 bit memory address
??? ;field.
?decfsz? loopcnt???????? ;Have we written all 64 locations?
?goto??? test1?????????? ;No, write another location.

??? ;Read loop:

?movlw?? .64???????????? ;Initialize loop counter.
?movwf?? loopcnt???????? ;
?movlw?? read??????????? ;Load W with the Read command.
?movwf?? cmd???????????? ;Transfer W into cmd register.
test2?? call??? see???????????? ;Read addressed data word from 93C46 device.
?movlw?? tstptrn???????? ;Load W with the pattern written.
?subwf?? highb,0???????? ;Verify the data read against what was
??? ;written.
?btfss?? status,***lag??? ;Same?
?goto??? errloop???????? ;No, error-out.
?movlw?? tstptrn???????? ;Repeat with the lower byte read.
?subwf?? lowb,0????????? ;
?btfss?? status,***lag??? ;Same?
?goto??? errloop???????? ;No, error-out.
?incf??? cmd???????????? ;Yes, both byte correct, increment the 6 bit
??? ;memory address field.
?decfsz? loopcnt???????? ;Have we read all 64 locations?
?goto??? test2?????????? ;No, read another location.

allok?? goto??? allok?????????? ;Home safe!

errloop goto??? errloop???????? ;Bad news!