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joshua_

Sat Feb 18 2006, 05:41AM

Registered Member #61 Joined: Thu Feb 09 2006, 05:50AM
Location: Mountain View, CA
Posts: 43

From time to time, you come across useful routines that do all that you need to set up some weird part of the microcontroller (or common part!) that you reference in all of your code. I'm sure they'd be useful to the rest of us; post them in this thread.

This is a fairly standard skeleton, but always helpful to have a pasteable source:

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
isr_save_ram    UDATA
ISR_STAT        RES     01
ISR_BSR         RES     01
ISR_W           RES     01

reset_vec       CODE 0x00
        GOTO    start

inth_vec        CODE 0x08
        GOTO    isr

intl_vec        CODE 0x18
        GOTO    isr

main            CODE
start:
        ...

isr:
        MOVWF   ISR_W
        MOVFF   STATUS, ISR_STAT
        MOVFF   BSR, ISR_BSR

        MOVFF   ISR_BSR, BSR
        MOVF    ISR_W, W
        MOVFF   ISR_STAT, STATUS
        RETFIE
;;;;;;;;;;;;;;;;;;;;;;;;;;;;

Similarly useful is this UART bringup code:

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
UART    CODE

        GLOBAL  uart_init
uart_init:
        BSF             TRISC, 7                ; set port directions
        BCF             TRISC, 6

        BCF             PIE1, RCIE
        BCF             PIE1, TXIE

        BCF             BAUDCON, ABDEN  ; we'll set the baud rate
        BCF             TXSTA, BRGH             ; low speed
        BSF             BAUDCON, BRG16  ; 16bit baud rate
        MOVLW   (((32000000/19200)/16)-1) >> 8
        MOVF    SPBRGH
        MOVLW   (((32000000/19200)/16)-1) & 0xFF
        MOVF    SPBRG

        BCF             RCSTA, CREN             ; receive disable
        BCF             TXSTA, TXEN             ; transmit disable
        BCF             TXSTA, SYNC             ; async mode

        BSF             RCSTA, SPEN             ; enable the serial port

        BCF             TXSTA, RX9              ; 8bit tx
        BSF             TXSTA, TXEN             ; transmit enable

        BCF             RCSTA, RX9              ; 8bit rx
        BSF             RCSTA, CREN             ; receive enable

        puts    uart_init_initializing

        RETURN
uart_init_initializing:
        DB              "Alive!\r\n",0

        GLOBAL  uart_putc
uart_putc:
        BTFSS   TXSTA, TRMT
         GOTO   uart_putc
        MOVWF   TXREG
        RETURN

        GLOBAL  uart_puts
uart_puts:
        TBLRD*+
        MOVF    TABLAT,W
        BTFSC   STATUS, Z
         RETURN
        CALL    uart_putc
        GOTO    uart_puts

        END
;;;;;;;;;;;;;;;;;;;;;;;;

What have you guys got? I'm looking for a little bit of ADC sample code for my segway project.

Carbon_Rod

Sat Feb 18 2006, 06:01AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

The microchip forum is the place to start as they have seen it all:

I have been there more than a few times (like when some errata fails to be sent with the app-notes)

The problem with ASM is it does not like to port, the code will differ for the P16c, DSPIC, and PIC18LFxxxx.

Like some PIC18 chips use the 55h preamble code to set the baud rate automatically in the EUART,

Note microchip's "Application Maestro" is free and has good lib docs (even for the ASM auto-code.)

What chip(s) do you use?
Cheers,

joshua_

Sat Feb 18 2006, 06:18AM

Registered Member #61 Joined: Thu Feb 09 2006, 05:50AM
Location: Mountain View, CA
Posts: 43

Carbon_Rod wrote ...

The microchip forum is the place to start as they have seen it all:

I have been there more than a few times (like when some errata fails to be sent with the app-notes)

I took a look there once, but mostly dismissed it. I'll have to look again.

wrote ...

The problem with ASM is it does not like to port, the code will differ for the P16c, DSPIC, and PIC18LFxxxx.

Many PICs have similar startup sequences if they have the same type of peripheral -- they pretty much just glue the same logic blocks onto the bus, just in different permutations.

wrote ...

Note microchip's "Application Maestro" is free and has good lib docs (even for the ASM auto-code.)

I took a look into that. I have it on one of the machines that I've installed mplab on, and it seems to be horribly out of date and lacking in samples for lots of the parts. Or should I be downloading modules for it separately?

wrote ...

What chip(s) do you use?

When I sample, I usually go after the 18F2550s (FS-USB PICs) since they tend to have just about the right combination of stuff for me.

Steve Conner

Sat Feb 18 2006, 11:44PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I'm a 16F877 man, myself. I think the code joshua posted is for an 18 series since it uses the TBLRD instruction. It also mentions a "puts" macro which would need to be defined elsewhere.

I do a bunch of PIC programming as part of my job, and I do indeed have a bunch of standard skeleton routines, for things like initialisation, keypad scanning, LCD drivers, and quadrature encoders, that I copy and paste around as needed. I can't post any code here though since it's commercially sensitive.

Bjørn

Mon Feb 20 2006, 10:35AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Here is my 8x8 bit multiplication for PIC16xxx, it is only 11 instructions, uses no temporary variables and takes a constant 67 cycles. It is pretty optimal for low resource use, one cycle and one memory location can be saved if mulcnd is contained in W on entry. The basic method can be found in the Microchip application notes, but their implementation is not very optimal.

mul8x8s clrf    prodH
        movlw   .128
        movwf   prodL
        movfw   mulcnd
mulsl   rrf     mulplr
        skpnc
        addwf   prodH
        rrf     prodH
        rrf     prodL
        skpc
        goto    mulsl

Steve Conner

Mon Feb 20 2006, 12:11PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Cool, I always used the Microchip multiply routine that takes 77 cycles or whatever it is. Just one question, what is "movfw", is it a macro you defined somewhere else, or did you mean to type movwf?

Bjørn

Mon Feb 20 2006, 01:29PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

"movfw file" is what Microchip calls a "special instruction mnemonic" it is identical to "movf file,W" and is accepted by any MPASM compatible assembler.

I try to not specify the destination of an operation with ",W" or ",F" in cases that are obvious then I can easily spot the non obvious cases in the source code and I have less chance of mixing it up.

I find the Microchip assembly language a bit peculiar, but after I made my own system that I find logical I have no problems.

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