CRTC pin CUDISP is not connected to the Gate Array, so it has no effect on a barebone CPC or Plus machine.
However, this signal is present on provided to the expansion port. And it is used by the [[PlayCity]] and [[Play2CPC]] expansions.
== DISPTMG ==
|1||0||-||-
|-
|1||1||Read from selected internal 6845 register||Read only Only
|-
|}
|1||0||Read Status Register||Read Only
|-
|1||1||Read from selected internal 6845 register||Read only Only
|}
|1||0||-||-
|-
|1||1||Read from selected internal 6845 register||Read only Only
|-
|}
|1||0||Read from selected internal 6845 register||Read Only
|-
|1||1||Read from selected internal 6845 register||Read only Only
|-
|}
* The CRTC is not connected to the CPU's RD and WR pins, so the CRTC is not aware of the CPU bus I/O direction. Therefore, if a read instruction is used on a write register of the CRTC, then a data is sent to the CRTC.
* On type types 0 and 1, if a Write Only register is read from, "0" is returned.
* CRTC types 3 and 4 are identical in every way, except for the unlocking mechanism specific to the ASIC.
* See the document "Extra CPC Plus Hardware Information" for more details.