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README.md

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+# BUILD
+
+You'll need
+
+- [A85 assembler](https://github.com/glitchwrks/a85)
+- [ZMAC assembler](http://48k.ca/zmac.html)
+- [monobit font converter](https://github.com/robhagemans/monobit)
+- `make`, `srecored`, `iconv` from your distribution's package repository
+
+# INSTALL
+
+Burn either 27c512.hex, 27c256.hex, 27c128.hex or 27c64.hex to your EPROM chip.
+
+# USE
+
+## CP/M disk format
+
+CBIOS expects CF card to be formatted with MBR using LBR addressing and up to 4 primary partions of type `52h` and size up to 8MB each. First 'track' of a partiotion is sytem track, put CCP+BDOS there, so CP/M can boot. You can access filesystem on these partitions or partition images from PC using either
+
+- [cpmtools](http://www.moria.de/~michael/cpmtools/)
+- [cpmfuse](http://www.nyangau.org/cpmfuse/cpmfuse.htm)
+- [cpmcbfs](http://www.nyangau.org/cpmcbfs/cpmcbfs.htm)
+
+`cpmtools`-compatible disk definition:
+```
+diskdef pac80
+  seclen 512
+  tracks 1024
+  sectrk 16
+  blocksize 8192
+  maxdir 512
+  skew 0
+  boottrk 1
+  os 2.2
+end
+```
+
+## MEMORY MAP
+
+256K memory space is divided to 16 16KB-pages. 64KB CPU address space is divided to 4 16KB-banks. Each bank can be mapped to any page. After reset all banks are mapped to page 0. Video memory starts at 1810h offset in each video page/plane. Column 0 at 1810h-18ffh, column 1 at 1910h-19ffh, and so on, total 40 columns. Plane 0 color is navy blue, plane 1 color is sand, both planes together give white.
+
+|Page|Type|Notes                            |
+|----|----|---------------------------------|
+|0   |RAM |                                 |
+|1   |RAM |                                 |
+|2   |RAM |                                 |
+|3   |RAM |                                 |
+|4   |RAM |video page 0 plane 0 at 1810-3fff|
+|5   |RAM |video page 0 plane 1 at 1810-3fff|
+|6   |RAM |video page 1 plane 0 at 1810-3fff|
+|7   |RAM |video page 1 plane 1 at 1810-3fff|
+|8   |RAM |optional                         |
+|9   |RAM |optional                         |
+|a   |RAM |optional                         |
+|b   |RAM |optional                         |
+|c   |RAM |optional                         |
+|d   |RAM |optional                         |
+|e   |RAM |optional                         |
+|f   |ROM |                                 |
+
+## I/O PORTS
+
+|Port |Assigned to        |
+|-----|-------------------|
+|00-07|EXT0               |
+|10-17|EXT1               |
+|20-27|EXT2               |
+|30-37|CF                 |
+|08   |BANK0              |
+|48   |BANK1              |
+|88   |BANK2              |
+|c8   |BANK3              |
+|1a   |PPI PORT A         |
+|1b   |PPI PORT B (SEL=1) |
+|19   |PPI PORT B (SEL=0) |
+|1c   |PPI PORT C         |
+|1d   |PPI CONTROL        |
+|28   |UART DATA          |
+|29   |UART CONTROL/STATUS|
+|38   |PSG                |
+
+## 8255 ports
+
+|   |Function|SEL=0|SEL=1|2nd 0|2nd 1|3rd 0|3rd 1|4th 0|4th 1|
+|---|--------|-----|-----|-----|-----|-----|-----|-----|-----|
+|PB0|gamepad |UP   |UP   |UP   |UP   |0    |Z    |1    |UP   |
+|PB1|gamepad |DOWN |DOWN |DOWN |DOWN |0    |Y    |1    |DOWN |
+|PB2|gamepad |0    |LEFT |0    |LEFT |0    |X    |1    |LEFT |
+|PB3|gamepad |0    |RIGHT|0    |RIGHT|0    |MODE |1    |RIGHT|
+|PB4|gamepad |A    |B    |A    |B    |A    |B    |A    |B    |
+|PB5|gamepad |START|C    |START|C    |START|C    |START|C    |
+|PB6|gamepad |0    |1    |0    |1    |0    |1    |0    |1    |
+|PB7|always=1|1    |1    |1    |1    |1    |1    |1    |1    |
+
+|   |WRITE                    |READ                      |
+|---|-------------------------|--------------------------|
+|PC0|video page               |video page                |
+|PC1|VBLANK interrupt enable  |VBLANK interrupt enable   |
+|PC2|UART interrupt enable    |UART interrupt enable     |
+|PC3|                         |keyboard interrupt request|
+|PC4|keyboard interrupt enable|keyboard strobe           |
+|PC5|                         |keyboard input buffer full|
+|PC6|                         |VBLANK interrupt request  |
+|PC7|                         |UART interrupt request    |