
CRT Controller Registers
9-7
`efmp69030 Databook
Revision 1.3 11/24/99
CR05
Horizontal Sync End Register
read/write at I/O address 3B5h/3D5h with index at address 3B4h/3D4h set to 05h
shadowed for pipelines A and B
7
Horizontal Blanking End Bit 5
This bit provides either the most significant bit of a 6-bit value or the 3rd most significant bit
of an 8-bit value that specifies the end of the horizontal blanking period relative to its
beginning.
In standard VGA modes, where bit 0 of the I/O Control Register (XR09) is set to 0, the
horizontal blanking end is specified with a 6-bit value. The 5 least significant bits of this
value are supplied by bits 4-0 of the Horizontal Blanking End Register (CR03), and the most
significant bit is supplied by this bit of this register.
In extended modes, where bit 0 of the I/O Control Register (XR09) is set to 1, the horizontal
blanking end is specified with an 8-bit value. The 5 least significant bits of this value are
supplied by bits 4-0 of the Horizontal Blanking End Register (CR03), the next most
significant bit is supplied by this bit of this register, and the 2 most significant bits are
supplied by bits 7 and 6 of the Extended Horizontal Blanking End Register (CR3C).
This 6-bit or 8-bit value should be programmed to be equal to the least significant 6 or 8
bits, respectively, of the result of adding the length of the blanking period in terms of
character clocks to the value specified in the Horizontal Blanking Start Register (CR02).
6-5
Horizontal Sync Delay
These bits define the degree to which the start and end of the horizontal sync pulse are
delayed to compensate for internal pipeline delays.
These 2 bits describe the delay in terms of a number of character clocks.
4-0
Horizontal Sync End
These 5 bits provide the 5 least significant bits of a 6-bit value that specifies the end of the
horizontal sync pulse relative to its beginning. In other words, this 6-bit value specifies the
width of the horizontal sync pulse. Bit 7 of Horizontal Sync End Register (CR05) supplies
the most significant bit.
This 6-bit value should be set to the least significant 6 bits of the result of adding the width
of the sync pulse in terms of character clocks to the value specified in the Horizontal Sync
Start Register (CR04).
76543
210
A
Hor Blnk
End Bit 5
Horizontal Sync Delay
Horizontal Sync End
B
Hor Blnk
End Bit 5
Horizontal Sync Delay
Horizontal Sync End
Bit
6 5
Amount of Delay
0 0
no delay
0 1
delayed by 1 character clock
1 0
delayed by 2 character clocks
1 1
delayed by 3 character clocks