Hi!
I'm C128 and C64 programmer and both machines have $0000 and $0001 as data direction registers.
They're different in some parts but function is same.
My Q is:
C64 allows to control Kernal and Basic ROM overlay in RAM by $0001.
What a function have these addresses in VIC20 and is possible anything like in C64 with Kernal and Basic overlay?
Thank you for your support.
I'm on VIC20 beginner.
Miro
$0000/$0001 data direction registers - VIC20?
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- Vic 20 Newbie
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Re: $0000/$0001 data direction registers - VIC20?
Zero page locations $0000 and $0001 are plain memory on the VIC-20. They hold a $4C (JMP) and the LSB of a user-defined routine to be called by the USR() command. This is comparable with the addresses $0310 and $0311 on the C64.
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- Vic 20 Newbie
- Posts: 12
- Joined: Fri Oct 28, 2016 8:21 pm
- Website: http://www.mirkosoft.sk
- Location: Slovakia
Re: $0000/$0001 data direction registers - VIC20?
Ok, understand. So, no any direction register.
Miro
Miro
- Mike
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Re: $0000/$0001 data direction registers - VIC20?
Just to set straight the terminology used here:
$00 and $01 on the 6510/7501/8502 provide the CPU I/O port. Of these two registers, $00 is the data direction register, $01 is the port data register. The 6502 CPU, used in the VIC-20, doesn't feature this CPU I/O port.
Neither, for that matter, does an unmodified VIC-20 provide the capability to have RAM 'under' BASIC, KERNAL and character ROM. This has just recently been discussed here in Denial, though for other reasons.
Further info:
Michael
$00 and $01 on the 6510/7501/8502 provide the CPU I/O port. Of these two registers, $00 is the data direction register, $01 is the port data register. The 6502 CPU, used in the VIC-20, doesn't feature this CPU I/O port.
Neither, for that matter, does an unmodified VIC-20 provide the capability to have RAM 'under' BASIC, KERNAL and character ROM. This has just recently been discussed here in Denial, though for other reasons.
Further info:
- "Ultimem BLK6",
- "Custom Char Set and Memory", and
- "Upgrade a VIC 20 to a C64, possible via expansion slot?".
Michael