Changes
CRTC
,/* CRTC Differences */
|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
|}
It is not possible to read from all the internal registers, this table shows the read/write status of each register for each type:
{|{{Prettytable|width: 700px; font-size: 2em;}}|rowspan=2|''Register Index ''||rowspan=2|''Register Name ''||colspan=4|''Type '' |-|0 ||1 ||2 ||3 |-|0 ||Horizontal Total ||Write Only ||Write Only ||Write Only ||(note 2) |-|1 Horizontal Displayed ||Write Only ||Write Only ||Write Only ||(note 2) |-2 Horizontal Sync Position ||Write Only ||Write Only ||Write Only ||(note 2) |-3 Horizontal and Vertical Sync Widths ||Write Only ||Write Only ||Write Only ||(note 2) |-4 Vertical Total ||Write Only ||Write Only ||Write Only ||(note 2) |-5 Vertical Total Adjust ||Write Only ||Write Only ||Write Only ||(note 2) |-6 Vertical Displayed ||Write Only ||Write Only ||Write Only ||(note 2) |-7 Vertical Sync position ||Write Only ||Write Only ||Write Only ||(note 2) |-8 Interlace and Skew ||Write Only ||Write Only ||Write Only ||(note 2) |-9 Maximum Raster Address ||Write Only ||Write Only ||Write Only ||(note 2) |-10 ||Cursor Start Raster ||Write Only ||Write Only ||Write Only ||(note 2) |-11 ||Cursor End Raster ||Write Only ||Write Only ||Write Only ||(note 2) |-12 ||Display Start Address (High) ||Read/Write ||Write Only ||Write Only ||Read/Write ||(note 2) |-13 ||Display Start Address (Low) ||Read/Write ||Write Only ||Write Only Read/Write ||(note 2) |-14 ||Cursor Address (High) ||Read/Write ||Read/Write ||Read/Write ||Read/Write ||(note 2) ***check |-
15 Cursor Address (Low) Read/Write Read/Write Read/Write Read/Write (note 2) **check
|-
16 Light Pen Address (High) Read Only Read Only Read Only Read Only (note 2) **check
|-
17 Light Pen Address (High) Read Only Read Only Read Only Read Only (note 2) **check
|-
|}
'''Notes: '''
On type 0 and 1, if a Write Only register is read from, "0" is returned.
