;********************************************************************
;*                      PICALC Directives Section                   *
;********************************************************************

	SUBTITL "93C46 3 WIRE INTERFACE ROUTINE"
	LIST     P=16C54,N=40,C=132


;********************************************************************
;*                      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.
zflag   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