Difference between revisions of "CRTC"
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| − | [[Category:Hardware]] | + | [[Category:Hardware]]__NOTOC__ |
| − | + | The 6845 CRTC controls how the display is generated. It is written to with | |
| − | + | [[VDU 23|VDU 23,0]] which also takes account of the current *TV and VDU 23,1 | |
| − | + | settings. The hardware is directly accessible at &FE00 and &FE01. | |
| − | + | The 6845 is used in the BBC, Master and System computers. Other display | |
| − | + | hardware is used on the Atom, Electron, and later computers | |
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Most systems without a hardware 6845 CRTC implement setting the cursor state | Most systems without a hardware 6845 CRTC implement setting the cursor state | ||
with registers 10 and 11 via VDU 23;10 and VDU 23;11. | with registers 10 and 11 via VDU 23;10 and VDU 23;11. | ||
| + | ==Summary== | ||
| + | <table><tr valign="top"> | ||
| + | <td> | ||
| + | * &FE00 - Select register | ||
| + | * &FE01 - Write to register | ||
| + | * [[CRTC#0|0]] - Horizontal total | ||
| + | * [[CRTC#1|1]] - Horizontal displayed | ||
| + | * [[CRTC#2|2]] - Horizontal sync position | ||
| + | * [[CRTC#3|3]] - Sync widths | ||
| + | * [[CRTC#4|4]] - Vertical total | ||
| + | * [[CRTC#5|5]] - Vertical total adjust | ||
| + | * [[CRTC#6|6]] - Vertical displayed | ||
| + | * [[CRTC#7|7]] - Vertical sync position | ||
| + | * [[CRTC#8|8]] - Interlace/Display delay/Cursor delay | ||
| + | * [[CRTC#9|9]] - Scan lines per character | ||
| + | * [[CRTC#10|10]] - Cursor start line and blink type | ||
| + | * [[CRTC#11|11]] - Cursor end line | ||
| + | <td> | ||
| + | * &FE00 - Read from status | ||
| + | * &FE01 - Read from register | ||
| + | * [[CRTC#12|12]] - Screen start address | ||
| + | * [[CRTC#13|13]] - Screen start address | ||
| + | * [[CRTC#14|14]] - Cursor position | ||
| + | * [[CRTC#15|15]] - Cursor position | ||
| + | * [[CRTC#16|16]] - Light pen position | ||
| + | * [[CRTC#17|17]] - Light pen position | ||
| + | * [[CRTC#18|18]] - Cursor width (extension) | ||
| + | * [[CRTC#19|19]] | ||
| + | * [[CRTC#19|20]] | ||
| + | * [[CRTC#19|21]] | ||
| + | * [[CRTC#19|22]] | ||
| + | * [[CRTC#31|31]] - Register 31 | ||
| + | </table> | ||
| + | |||
| + | ===&FE00 - Register number=== | ||
| + | ===&FE01 - Register data=== | ||
| + | |||
| + | ===Register 0 - Horizontal total=== | ||
| + | ===Register 1 - Horizontal displayed=== | ||
| + | ===Register 2 - Horizontal sync position=== | ||
| + | ===Register 3 - Sync widths=== | ||
| + | ===Register 4 - Vertical total=== | ||
| + | ===Register 5 - Vertical total adjust=== | ||
| + | ===Register 6 - Vertical displayed=== | ||
| + | ===Register 7 - Vertical sync position=== | ||
| + | ===Register 8 - Interlace/Display delay/Cursor delay=== | ||
| + | ===Register 9 - Scan lines per character=== | ||
| + | ===Register 10 - Cursor start line and blink type=== | ||
| + | ===Register 11 - Cursor end line=== | ||
| + | ===Register 12/13 - Screen start address=== | ||
| + | ===Register 14/15 - Cursor position=== | ||
| + | ===Register 16/17 - Light pen position=== | ||
| + | ===Register 18 - Cursor width=== | ||
| + | ===Register 19 -=== | ||
| + | ===Register 20 -=== | ||
| + | ===Register 31 - Register 31=== | ||
| + | |||
| + | ==Extensions== | ||
| + | Extensions to the VDU 23,0 interface, or extended hardware, should probably used | ||
| + | register numbers 128 upwards. | ||
| + | |||
| + | ==Hardware differences== | ||
| + | There are several slightly different versions of the 6845. The BBC series | ||
| + | require a 6845S varient as the VDU drivers depend on certain functionality: | ||
| + | * R3 Vertical Sync | ||
| + | * R6 Vertical Displayed any odd/even value, to set to 25 in MODE 3,6,7. | ||
| + | * R8 Display Delay timing for MODE 7 | ||
[[User:Jgharston|Jgharston]] 14:47, 24 December 2007 (UTC) | [[User:Jgharston|Jgharston]] 14:47, 24 December 2007 (UTC) | ||
| + | [[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 03:01, 15 January 2023 (CET) | ||
Revision as of 04:01, 15 January 2023
The 6845 CRTC controls how the display is generated. It is written to with VDU 23,0 which also takes account of the current *TV and VDU 23,1 settings. The hardware is directly accessible at &FE00 and &FE01. The 6845 is used in the BBC, Master and System computers. Other display hardware is used on the Atom, Electron, and later computers
Most systems without a hardware 6845 CRTC implement setting the cursor state with registers 10 and 11 via VDU 23;10 and VDU 23;11.
Summary
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&FE00 - Register number
&FE01 - Register data
Register 0 - Horizontal total
Register 1 - Horizontal displayed
Register 2 - Horizontal sync position
Register 3 - Sync widths
Register 4 - Vertical total
Register 5 - Vertical total adjust
Register 6 - Vertical displayed
Register 7 - Vertical sync position
Register 8 - Interlace/Display delay/Cursor delay
Register 9 - Scan lines per character
Register 10 - Cursor start line and blink type
Register 11 - Cursor end line
Register 12/13 - Screen start address
Register 14/15 - Cursor position
Register 16/17 - Light pen position
Register 18 - Cursor width
Register 19 -
Register 20 -
Register 31 - Register 31
Extensions
Extensions to the VDU 23,0 interface, or extended hardware, should probably used register numbers 128 upwards.
Hardware differences
There are several slightly different versions of the 6845. The BBC series require a 6845S varient as the VDU drivers depend on certain functionality:
- R3 Vertical Sync
- R6 Vertical Displayed any odd/even value, to set to 25 in MODE 3,6,7.
- R8 Display Delay timing for MODE 7
Jgharston 14:47, 24 December 2007 (UTC) Jgharston (talk) 03:01, 15 January 2023 (CET)
