M69000 Asiliant Technologies, M69000 Datasheet - Page 117

• Manufacturer Part Number: M69000
• Manufacturer: Asiliant Technologies

Specifications of M69000

• Lead Free Status / Rohs Status: Supplier Unconfirmed

9-24
CR15
read/write at I/O address 3B5h/3D5h with index at address 3B4h/3D4h set to 15h
7-0
CR16
read/write at I/O address 3B5h/3D5h with index at address 3B4h/3D4h set to 16h
7-0
&+,36
7
7
Vertical Blanking Start Bits 7-0
This register provides the 8 least significant bits of either a 10-bit or 12-bit value that specifies the
beginning of the vertical blanking period relative to the beginning of the active display area of the
screen. Whether this value is described in 10 or 12 bits depends on the setting of bit 0 of the I/O
Control Register (XR09).
In standard VGA modes, where bit 0 of the I/O Control Register (XR09) is set to 0, the vertical
blanking start is specified with a 10-bit value. The most and second-most significant bits of this
value are supplied by bit 5 of the Maximum Scanline Register (CR09) and bit 3 of the Overflow
Register (CR07), respectively.
In extended modes, where bit 0 of the I/O Control Register (XR09) is set to 1, the vertical blanking
start is specified with a 12-bit value. The 4 most significant bits of this value are supplied by bits 3-
0 of the Extended Vertical Blanking Start Register (CR33).
This 10-bit or 12-bit value should be programmed to be equal to the number of scanlines from the
beginning of the active display area to the beginning of the vertical blanking period. Since the active
display area always starts on the 0th scanline, this number should be equal to the number of the
scanline on which vertical blanking begins, minus one.
Vertical Blanking End Bits 7-0
This register provides a 8-bit value that specifies the end of the vertical blanking period relative to
its beginning.
This 8-bit value should be set equal to the least significant 8 bits of the result of adding the length
of the vertical blanking period in terms of the number of scanlines that occur within the length of the
vertical blanking period to the value that specifies the beginning of the vertical blanking period (see
the description of the Vertical Blanking Start Register for details).
69000 Databook
Vertical Blanking Start Register
Vertical Blanking End Register
6
6
5
5
Subject to Change Without Notice
Vertical Blanking Start Bits 7-0
Vertical Blanking End Bits 7-0
CRT Controller Registers
4
4
3
3
2
2
Revision 1.3 8/31/98
1
1
0
0