4. As far as I know, the KC compact used HD6845S only.
The 6845 is selected when bit 14 of the I/O port address is set to "0". Bit 1 and 0 of the I/O port address define the function to access. The remaining bits can be any value, but it is adviseable to set these to "1" to avoid conflict with other devices in the system.
The recommended I/O port addressess are: I/O port address Function Read/Write &BCxx Select 6845 register Write only &BDxx Write 6845 register data Write only &BExx (note 1) Read only &BFxx (note 1) Read only
{|{{Prettytable|width: 700px; font-size: 2em;}}
|''I/O port address''||''Function''||''Read/Write''
|-
|&BCxx||Select 6845 register||Write only
|-
|&BDxx||Write 6845 register data||Write only
|-
|&BExx||(note 1)||Read only
|-
|&BFxx||(note 1)||Read only
|-
|}
NOTE:
1. The function of these I/O ports is dependant on the CRTC type
Signals
The following table defines the generated memory address from the CRTC and Gate-Array signals.
On type 0 and 1, if a Write Only register is read from, "0" is returned.
See the document "Extra CPC Plus Hardware Information" for more details.
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