Canon A-200 series Service Manual page 102

• Video
Output
Timing
The V-RAM is accessed by the CPU and the CRTC alternately. Switching between the CRT mode
and the CRTC mode is performed by the CPU/CRTC ciock signal.
When in the CRTC mode, the CPU/CRTC ciock signal becomes the OE signal to the 6116 and
as a result, a data is. output to the bus.
This data is latched at the rising edge of the CPU/CRTC clock signal and finally, this latched sig ­
nal becomes an address for the Character Generator (2364).
Since the 2364 can always be accessed, it output a data on to the data bus when the address
is determined. This data is input to the shift register (LS166) when the S/L signal is LOW, and
is output at the next OSC clock after it is shifted corresponding to everyone pixel on the screen.
As well as the CH (Character) signal, the AT (Attribute) signal is output when in the CRTC mode.
A data output from the 6116 is latched at rising edge
of
the CPU/CRTC clock signal.
A dot signal output from the shift register and this attribute signal are mixed and latched at the
rising edge of the next OSC clock signal. This latched signal becomes the video output.
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