topic Re: HSC08 assembly code in 8-bit Microcontrollers

HSC08 assembly code

hityou123 — Wed, 05 Dec 2012 20:06:15 GMT

I am doing assembly after a long time. Need some guidance -

To load HX register from RAM,

I do LDHX ram. This should load (ram) to X and (ram+1) to H

correct?

I am trying to write code for a clock. I increment "RTCSEC" . When the value is 30d, that's equal to 30seconds.

At every 30secs, I increment RTCMIN. When RTCMIN is 120, I increment RTCHR. If the RTCMIN is not equal to 120, the code branches to incRTCMIN.

Is this correct?

inc RTCSEC

lda RTCSEC

cmp #$1E ; 30 seconds

beq incRTCMIN

What to put here???

incRTCMIN: clr RTCSEC

inc RTCMIN

lda RTCMIN

cmp #$78 ; 120 mins make an hour (since 30 secs make a min)

beq incRTCHR

bra incRTCMIN

Re: HSC08 assembly code

Derrick — Thu, 06 Dec 2012 20:36:10 GMT

It's the other way around:

ldhx RAM ; H = (RAM) and X = (RAM + 1)

As for your code stub, I'm going to guess that this will be run as part of an interrupt service routine (ISR) that gets executed once a second(?). Make sure that you clear the source of the interrupt before you exit the ISR. I'm not sure why you're only counting to 30 seconds, but I'm guessing that you don't need to display these values. If that's the case, decrementing variables can be more efficient. If I assume that this is correct, and that your variables are located in direct page, I suggest considering something like this:

INIT_RTCSEC: equ $1E ; initial value for RTCSEC = 30

INIT_RTCMIN: equ $78 ; initial value for RTCMIN = 120

init_clock:

mov #INIT_RTCSEC, RTCSEC ; initialize RTCSEC

mov #INIT_RTCMIN, RTCMIN ; initialize RTCMIN

rts ; return

ISR_clock:

;

; clear the source of the interrupt

;

dbnz RTCSEC, ISR_clock_exit ; decrement RTCSEC and exit if it's not zero

mov #$1E, RTCSEC ; else, reload RTCSEC with 30

dbnz RTCMIN, ISR_clock_exit ; decrement RTCMIN and exit if not zero

mov #$78, RTCMIN ; else, reload RTCMIN with 120

inc RTCHR ; advance RTCHR

ISR_clock_exit:

rti ; exit

I hope that this helps.

Best Regards,

Derrick

Re: HSC08 assembly code

bigmac — Sat, 08 Dec 2012 17:21:36 GMT

Hello Derrick,

The assembly code for an "incrementing" solution might be as follows:

ORG Z_RAMStart

...

RTCSEC: DS.B 1

RTCMIN: DS.B 1

RTCHR: DS.B 1

ORG ROMStart

...

; Increment RTC registers

RTC_INCR: INC RTCSEC

LDA RTCSEC

CMP #30

BLO RI1

CLR RTCSEC

INC RTCMIN

LDA RTCMIN

CMP #120

BLO RI1

CLR RTCMIN

INC RTCHR

RI1: RTS

Decimal (rather than hexadecimal) constants may be used within the code, where these make more sense. If you are using a timer interrupt, the above subroutine could be called from within the associated ISR.

Regards,

Mac

Re: HSC08 assembly code

hityou123 — Mon, 10 Dec 2012 12:37:36 GMT

Derrick,

In the HX register, H is the MSByte and X is the LSbyte?

The HCS08 is big endian? unlike the 8085 which is little endian.

One more question -

How do I move a value to RAM ?

Mov #$02, RAM_location

Re: HSC08 assembly code

Derrick — Thu, 10 Jan 2013 15:12:55 GMT

Yes, H is the MSB and X is the LSB of the 16-bit Index Register.

The endian is the opposite of the 8085. This makes it a little easier to see 16- and 32-bit values in a memory dump (but everyone has their own preferences).

Using the MOV instruction requires that either the source address and/or the destination address be in the Direct Page (i.e., 0x0000 to 0x00FF inclusive). This is why it works when accessing (most) peripheral registers. So your value in RAM needs to be located in the Direct Page for your example to work.

Best Regards,

Derrick

(I apologize for the late response - I had a busy holiday season :smileyhappy:)