Changes
CRTC
,/* CRTC register differences */
This table lists the known ICs used, with their part number, manufacturer and type number.
{|{{Prettytableclass="wikitable"|width: 700px; font-size: 2em;}}|''!Part number''||''!Manufacturer''||''!Type number (note 3)''
|-
|HD6845S||Hitachi||0
The recommended I/O port addresses are
{|{{Prettytableclass="wikitable"|width: 700px; font-size: 2em;}}|''!I/O port address''||''!Function''||''!Read/Write''
|-
|&BCxx||Select 6845 register||Write only
The video memory address VMA of the [[Gate Array]] is constructed from the CRTC MA and RA signals.
{|{{Prettytableclass="wikitable"|width: 700px; font-size: 2em;}}|''!Video Memory Address''||''!Signal source''||''!Signal name''
|-
|A15||6845||MA13
The Internal registers of the 6845 are:
{|{{Prettytableclass="wikitable"|width: 700px; font-size: 2em;}}|''!Register Index''||''!Register Name''||''!Range''||''!CPC Setting''||''!Notes''
|-
|0||Horizontal Total (-1)||00000000||63||Width of the screen, in characters. Should always be 63 (64 characters). 1 character == 1μs.
Type 0
{|{{Prettytable|width: 700px; font-size: 2em;}}class="wikitable"|''!b1''||''!b0''||''!Function''||''!Read/Write''
|-
|0||0||Select internal 6845 register||Write Only
Type 1
{|{{Prettytable|width: 700px; font-size: 2em;}}class="wikitable"|''!b1''||''!b0''||''!Function''||''!Read/Write''
|-
|0||0||Select internal 6845 register||Write Only
Type 2
{|{{Prettytable|width: 700px; font-size: 2em;}}class="wikitable"|''!b1''||''!b0''||''!Function''||''!Read/Write''
|-
|0||0||Select internal 6845 register||Write Only
Type 3 and 4
{|{{Prettytable|width: 700px; font-size: 2em;}}class="wikitable"|''!b1''||''!b0''||''!Function''||''!Read/Write''
|-
|0||0||Select internal 6845 register||Write 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;}}class="wikitable"|!rowspan=2|''Register Index''||!rowspan=2|''Register Name''||!colspan=3|''Type''
|-
|-
|0||Horizontal Total (-1)||colspan=3 style="text-align: center;"|Write Only
On CRTCs 3/4, only the 3 least significant bits of the selected register number are considered to read a register according to the following table:
{|{{Prettytable|width: 700px; font-size: 2em;}}class="wikitable"|'''!Nb'''||'''!Register'''||'''!Definition'''
|-
|0||R16||Light Pen Address (High)
The cursor raster registers R10/R11 act as status registers when read on CRTCs 3/4. They behave as normal cursor raster registers upon write.
{| class="wikitable sortable"
! R10 - Bit number
! Bit value
|}
{| class="wikitable sortable"
! R11 - Bit number
! Bit value
