== CRTC register differences ==
The following tables list the functions that can be accessed for each type:
Types 0/2:
{| class="wikitable"
!b1
!b0
!Function
!Read/Write
|-
|0||0||Select internal 6845 register||Write Only
|-
|0||1||Write to selected internal 6845 register||Write Only
|-
|1||0||-||-
|-
|1||1||Read from selected internal 6845 register||Read Only
|-
|}
Type 1:
{| class="wikitable"
!b1
!b0
!Function
!Read/Write
|-
|0||0||Select internal 6845 register||Write Only
|-
|0||1||Write to selected internal 6845 register||Write Only
|-
|1||0||Read Status Register||Read Only
|-
|1||1||Read from selected internal 6845 register||Read Only
|}
Types 3/4:
{| class="wikitable"
!b1
!b0
!Function
!Read/Write
|-
|0||0||Select internal 6845 register||Write Only
|-
|0||1||Write to selected internal 6845 register||Write Only
|-
|1||0||Read from selected internal 6845 register||Read Only
|-
|1||1||Read from selected internal 6845 register||Read Only
|-
|}
It is not possible to read from all the internal registers, this table shows the read/write status of each register for each type:
