; term.asm

; Program to talk to the Raven serial port monitor.  When run, it sends a message to the
; monitor, and then will echo any characters or strings sent and display the characters
; on the led bar.
;
; This is pretty crude, and would be much better if transmit data were double buffered
; to increase speed (probably not much advantage at 9600 baud) and using interrupts would
; make it much more flexible.

        LIST P=16F877, R=DEC

        INCLUDE "P16F877.inc"


; Definitions for the PIC

RX         EQU   7     ; PORT C bit for SDA
TX         EQU   6     ; PORT C bit for SCL


RAM        EQU   0x20

Temp       EQU   RAM+0
Counter    EQU   RAM+1
DTemp1     EQU   RAM+2
DTemp2     EQU   RAM+3
DTemp3     EQU   RAM+4
Char       EQU   RAM+5
           


; Start of the Program

        ORG       3
        goto      Start

        ORG       0x20

; Message
Msg     
        addwf     PCL,F
        DT        "Hi Hal"

; Simple ASCII conversion table

GetASCII
        movwf     Temp
        movlw     65
        subwf     Temp,W
        addwf     PCL,F
        retlw     0x41        ; A
        retlw     0x42        ; B
        retlw     0x43        ; C
        retlw     0x44        ; D
        retlw     0x45        ; E
        retlw     0x46        ; F
        retlw     0x47        ; G
        retlw     0x48        ; H
        retlw     0x49        ; I
        retlw     0x4A        ; J
        retlw     0x4B        ; K
        retlw     0x4C        ; L
        retlw     0x4D        ; M
        retlw     0x4E        ; N
        retlw     0x4F        ; O
        retlw     0x50        ; P
        retlw     0x51        ; Q
        retlw     0x52        ; R
        retlw     0x53        ; S
        retlw     0x54        ; T
        retlw     0x55        ; U
        retlw     0x56        ; V
        retlw     0x57        ; W
        retlw     0x58        ; X
        retlw     0x59        ; Y
        retlw     0x5A        ; Z
Start

; Initialize the TRIS registers.  Importantly, SDA and SCL must be inputs

        bsf       STATUS, RP0
        clrf      TRISA               ; for led bar
        clrf      TRISD               ; for led bar
        bsf       TRISC,RX
        bcf       TRISC,TX
        bcf       STATUS, RP0

; Initialize the USART

        call      URTConfig

; The main loop just sends a few characters to the USART and displays what comes back on
; the led bar

mainloop

        movlw     6
        movwf     Counter
        movlw     0
        movwf     Temp

send_loop       
        movf      Temp,W
        call      Msg
        call      URTSend
        incf      Temp,F
        decfsz    Counter,F
        goto      send_loop

; Read characters, put on led bar and echo back forever

recv_loop
        call      URTReceive
        call      DispLedBar
        goto      recv_loop


; ---------------------------------------------------------
; Routines for managing USART communications

; Configure the interface
; Use 9600 baud, no parity asynchronous mode

URTConfig
        bsf       STATUS,RP0
        movlw     b'10100100'     ; master clock, 8-bit, xmit enabled, asynch, high baud rate
        movwf     TXSTA
        movlw     129             ; 9600 divisor for a 20 MHz clock
        movwf     SPBRG
        bcf       STATUS,RP0

        movlw     b'10010000'      ; enable serial port (necessary)
        movwf     RCSTA

        return

; Slow send.  Put the byte into TXREG and wait for transfer to shift register to complete.

URTSend
; Make sure the previous send is gone
        btfss     PIR1,TXIF
        goto      $-1

        movwf     TXREG
        return

; Wait for byte to arrive and then return it.

URTReceive
; Make sure that previous receive is done

        btfss     PIR1,RCIF
        goto      $-1

; Got a byte in the receive buffer - echo it and return
 
        movf      RCREG,W
        call      URTSend

        return

; ----------------------------------------------------------
; Display routines

; Routine to display something on the LED bank

DispLedBar

; Enable the led bar and put the value in W there.

        movwf     Temp             ; save W
        movlw     0x12
        movwf     PORTA

        comf      Temp,W
        movwf     PORTD

        return

; Display something on the Led Bar and wait for one second - 
; handy for debugging

DisplayDebug
        call      DispLedBar
        movlw     1
        call      Delay_sec

        END