Vic20 Startup sequence to main screen Display? (was: Help Cartridge with a startup SOUND)

[audronic1]

Hi All

I am New to Denial.
I with to find a Game - Rom That Starts up with Music- Sounds Noises upon Power up ?
WHY:- Because I have a Vic20 that is unwell and I only have a thought that it may be running.
and if I can put a Cart that starts up with some sound then this might help

I have repaired a lot of other machines BUT this Vic 20 is still a challenge

Thanks

Keep Safe

Ray

[audronic1]

Hi All

New User here.

Is their a document using simple terms the Vic20 Startup sequence to main screen Display ?

I have an unwell Vic20 (later version) FAB no. 251040-01, Assy No 250403, Revision D, 1982

and a startup sequence MAY help

Keep Safe

Ray

[srowe]

New User here.

Is their a document using simple terms the Vic20 Startup sequence to main screen Display ?

I have an unwell Vic20 (later version) FAB no. 251040-01, Assy No 250403, Revision D, 1982

and a startup sequence MAY help

Welcome.

The VIC-20 boots up like this:

• on reset the 6502 jumps to the vector at $FFFC
• the initial KERNAL routine looks for an autostart signature at $A004 and jumps to the vector at $A000 if a cartridge is present in BLK5
• otherwise it checks for the amount of RAM, on error it goes into a tight loop
• more initialization follows, VIAs, VIC
• finally, the KERNAL jumps to the BASIC vector in $C000

One test to try is a game cartridge (except the adventure ones). If that runs then the BASIC ROM is faulty.

[audronic1]

@srowe

Thanks for that.
Is there a link to that sort of information that goes little further ?

Keep Safe

Ray

[srowe]

Thanks for that.
Is there a link to that sort of information that goes little further ?

The best description in is the KERNAL disassembly

Code: Select all

14935 ;***********************************************************************************;
14936 ;
14937 ; RESET, hardware reset starts here
14938 
14939 START
14940         LDX     #$FF                    ; set .X for stack
14941         SEI                             ; disable interrupts
14942         TXS                             ; clear stack
14943         CLD                             ; clear decimal mode
14944         JSR     CHKAUTO                 ; scan for autostart ROM at $A000
14945         BNE     LAB_FD2F                ; if not there continue VIC startup
14946 
14947         JMP     (XROMCOLD)              ; call ROM start code
14948 
14949 LAB_FD2F
14950         JSR     INITMEM                 ; initialise and test RAM
14951         JSR     FRESTOR                 ; restore default I/O vectors
14952         JSR     INITVIA                 ; initialise I/O registers
14953         JSR     INITSK                  ; initialise hardware
14954         CLI                             ; enable interrupts
14955         JMP     (COLDST)                ; execute BASIC

https://eden.mose.org.uk/gitweb/?p=rom- ... EAD#l14939

[audronic1]

@ srowe

Thanks

Vic20 Kernal ROM Info - eden.mose.org.uk
That will be good to have a look at.

Keep Safe

Ray

[Mike]

I have an unwell Vic20 (later version) [...]

There's a slight lack of detail in your fault description, but then I think you are likely doing the fourth or fifth step of tests before the first when using a cartridge for checks.

Does the Power LED turn on? Do you get (just) a black screen or something else? Have you checked the supply voltages on the mainboard with a multimeter? 5 VDC within range? 9 VAC within range? Ripple on the 5 VDC below, say, 0.1 V? You can check the latter by switching the multimeter to AC while probing the 5V supply rail. The video chip is known to cease video generation as soon as there's excessive ripple on the 5V. Do you get a proper Reset pulse on Pin 40 of the 6502? Does any of the chips get excessively hot after a short time? Etc. ...

[audronic1]

Hi Mike

Various replies to your questions

Does the Power LED turn on?
:- Yes

Do you get (just) a black screen or something else?
:- Something else

See Photo

Have you checked the supply voltages on the mainboard with a multimeter? 5 VDC within range?
:- 4.93

9 VAC within range?
:- 10.8

Ripple on the 5 VDC below, say, 0.1 V?
:-0.9 Mv

Do you get a proper Reset pulse on Pin 40 of the 6502?
:- Yes tested about 2 Second Delay

Does any of the chips get excessively hot after a short time? Etc. ...
:- No all are OK

Some Photos below

Keep Safe

Ray

[bjonte]

You seem to get as far as the VIC chip initialization since you have something displayed with the correct number of volumns and rows. If you type on the keyboard, does the screen change in any way as a response?

You could try poking to change the border color or start a sound to see if only the display seems affected.

[srowe]

You seem to have socketed pretty much everything, from the screen I would say there's a fault in the address buffering between the VIC and the CPU. That would suggest UD1 and/or UD8/UE8.

https://portcommodore.com/rcarlsen/cbm/vic20/vic20.txt

[audronic1]

You seem to have socketed pretty much everything, from the screen I would say there's a fault in the address buffering between the VIC and the CPU. That would suggest UD1 and/or UD8/UE8.

https://portcommodore.com/rcarlsen/cbm/vic20/vic20.txt

@srowe

Thanks I will have a closer look at the UD1-UD8/UE9

and a reread of the Document By Ray Carlsen

Thanks

Keep Safe

Ray W

[audronic1]

You seem to get as far as the VIC chip initialization since you have something displayed with the correct number of volumns and rows. If you type on the keyboard, does the screen change in any way as a response?

You could try poking to change the border color or start a sound to see if only the display seems affected.

@bjonte

I will connect a keyboard.
as I am New to Vic 20's I don't know of any pokes yet
If you can help with the pokes that would be appreciated

Thanks

Keep Safe

Ray W

[srowe]

I will connect a keyboard.
as I am New to Vic 20's I don't know of any pokes yet
If you can help with the pokes that would be appreciated

Try just

Code: Select all

POKE36878,15
POKE36875,200

[audronic1]

You seem to get as far as the VIC chip initialization since you have something displayed with the correct number of volumns and rows. If you type on the keyboard, does the screen change in any way as a response?

You could try poking to change the border color or start a sound to see if only the display seems affected.

@bjonte

Keyboard does not show any change no matter what I press on the keyboard ( I also swapped the 6522s over no change.

I tested some Pokes :-

Poke 36878,15
Poke 36875,225

No Sound

Thanks for the thought

Keep Safe

Ray W

[audronic1]

I will connect a keyboard.
as I am New to Vic 20's I don't know of any pokes yet
If you can help with the pokes that would be appreciated

Try just

Code: Select all

POKE36878,15
POKE36875,200

@srowe

The pokes did not work , also changed the 6522s over still no output.

Thanks

Keep Safe

Ray W