n
/
cardiograph-computer
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Docs: Add dev notes on memory bank-switching

This commit is contained in:
n loewen 2023-08-15 15:38:09 +01:00
parent 6754725c9b
commit 245da348ea
1 changed files with 17 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
notes/2023-08-15--dev-notes.md
View File

@ -8,8 +8,9 @@
- [ ] Review planned changes to the system - [ ] Review planned changes to the system
- [x] CHP, CFC -> FHP, FTG -- dev note 2023-08-07 - [x] CHP, CFC -> FHP, FTG -- dev note 2023-08-07
- [/] bank-switching flag in 0 page
- added notes below, but decided to leave implementation for another day
- [ ] ? 5x5 display - [ ] ? 5x5 display
- [ ] bank-switching flag in 0 page
- [ ] Implement any changes necessary for writing a program? - [ ] Implement any changes necessary for writing a program?
- [ ] Write a program - [ ] Write a program
@ -19,4 +20,18 @@
Ken Shirriff, [The 6502 overflow flag explained mathematically](https://www.righto.com/2012/12/the-6502-overflow-flag-explained.html): Ken Shirriff, [The 6502 overflow flag explained mathematically](https://www.righto.com/2012/12/the-6502-overflow-flag-explained.html):
> A common definition of overflow is `V = C6 xor C7`. That is, overflow happens if the carry into bit 7 is different from the carry out. > A common definition of overflow is `V = C6 xor C7`. That is, overflow happens if the carry into bit 7 is different from the carry out.
## Bank switching
### Planned memory map
- `00-0F` - display (4x4)
- `10-1F` - keypad? (details TBD)
- `20 ` - pointer to display memory
- `21 ` - pointer to keypad memory
- `22 ` - pointer to memory bank
- `23-2F` - reserved for future use / variable storage
- `30 ` - initial value for IP
- `30-80` - free
- `80-FF` - free, can be bank-switched