M69030 Asiliant Technologies, M69030 Datasheet - Page 121

• Manufacturer Part Number: M69030
• Manufacturer: Asiliant Technologies

Specifications of M69030

• Operating Temperature (min): 0C
• Operating Temperature Classification: Commercial
• Operating Temperature (max): 70C
• Rad Hardened: No
• Lead Free Status / Rohs Status: Supplier Unconfirmed

CR0D
read/write at I/O address 3B5h/3D5h with index at address 3B4h/3D4h set to 0Dh
shadowed for pipelines A and B
7-0
`efmp
A
B

Start Address Bits 7-0
69030 Databook
7
Start Address Low Register
This register provides the eight least significant bits of either a 16-bit or 20-bit value that
specifies the memory address offset from the beginning of the frame buffer at which the
data to be shown in the active display area begins.
In standard VGA modes, where bit 0 of the I/O Control Register (XR09) is set to 0, the start
address is specified with a 16-bit value. The eight bits of the Start Address High Register
(CR0C) provide the eight most significant bits of this value, while the eight bits of this
register provide the eight least significant bits.
In extended modes, where bit 0 of the I/O Control Register (XR09) is set to 1, the start
address is specified with a 20-bit value. The four most significant bits are provided by bits
3-0 of the Extended Start Address Register (CR40), bits 15 through 8 of this value are
provided by the Start Address High Register (CR0C), and the eight least significant bits are
provided by this register. Note that in extended modes, these 20 bits are double-buffered
and synchronized to VSYNC to ensure that changes occurring on the screen as a result of
changes in the start address always have a smooth or instantaneous appearance. To
change the start address in extended modes, all three registers must be set for the new
value, and then bit 7 of CR40 must be set to 1. When this is done the hardware will update
the start address on the next VSYNC. When this update has been performed, the hardware
will set bit 7 of CR40 back to 0.
6
5
CRT Controller Registers
Start Address Bits 7-0
Start Address Bits 7-0
4
3
2
Revision 1.3 11/24/99
1
0
9-19