10. bit 2 = enable/disable MAPMOD (changes how colour is decoded and how mapper values are decoded), bit 3 = force video to black, bit 4 = Enable 8253 timer. Any I/O write then accesses 8253 with data comming from 8255 port A. Bit A0/A1 of I/O port defines 8253 register, bit 5 = if 0, then AY is accessed when read/write to 8255 port A, if 1 then real-time clock is accessed with read/write to 8255 port A. When real-time clock is selected, bits 3..0 of PPI port C are used to define real-time clock operation. DS bit 2, AS bit 1, R/W bit 0. So combinations are 2, write address, 4 write data, 5 read data.
== Keyboard ==
The Aleste uses a MSX keyboard, as seen by the characteristic five function keys. The mainboard contains some excessive TTL logic, assisted by the upper data bits of the VDKEY eprom, that translates the MSX matrix to a CPC matrix. So, at I/O port level, the CPU "sees" a CPC matrix, not a MSX matrix. When running MSXDOS, this leads to the funny situation that MSXDOS must undo the hardware MSX-to-CPC translation by some software CPC-to-MSX translation.
The keyboard has some additional keys, which aren't on normal CPC keyboards:
* '''F1/F6, F2/F7, F3/F8, F4/F9, F5/F10''' - MSX-style function keys, mapped to keyboard row 10, bits 7,6,5,4,3.
* '''HELP, INS, b''' - additional keys, mapped to keyboard row 10, bits 2,1,0.
* '''R/L''' - Russian/Latin mode, mapped to row 9, bit6 (aka joystick Fire3).
* '''RES''' - Reset button, goes to /RESET signal.
* '''Four unknown keys''' - These keys (above the numeric keypad) may be unused, or having same function as other keys?
The Aleste has a JCUKEN keyboard, rather than a QWERTY keyboard.
* '''Unknown''' if this done by hardware, or by patched CPC bios (?)
* Normally, the key next to TAB '''should''' be Row8.Bit3 in the CPC matrix. And the BIOS should assign "Q" to it for QWERTY keyboards (or "J" for JCUKEN keyboards).
== Technical specs ==