Canon A-200 series Service Manual page 93

• V-RAM
The monochrome .display adapter board has 4K bytes of V-RAM.
2K of 4K bytes store character codes corresponding to the characters to be displayed on the
screen, and other 2K bytes are used for storage of attribute codes. Unlike the system RAM on
the main board, the V-RAM has no parity bits.
The V-RAM area is assigned at the address BOOOOH and upper.
110 Address
Description
3B4
68B45 Index register
3B5 68B45 Data register
3B8 CRT Control port
3BA CRT Status port
Table 6-14
Further, 3B8 and 3BA are assigned as follows:
1/0
Address
Bit Description
3B8 0 High resolution mode
3 Video enable
6 Blink enable
Table 6-15
Unless the address 3B8 is
"01':
OSC signal in not output and as a result, nothing is displayed
on the screen.
I/O Address Bit Description
3BA 0 H-sync
3
B/W video
Table 6-16
This port is used to check the monochrome display adaptor board. That is, whether the H-sync
or BIW video signal is output or not is judged through this port.
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