AMT Datasouth Accel-7350 Service Manual page 78

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BBG030 pin assignment
Regarding DMA
BBG010 transfers printing data to BBG010 directly by DMA from DRAM without going
through the CPU in order to transmit data developed in DRAM to BBG010 from DRAM at
high speed (DMA: Direct Memory Access). The following is an explanation of this process.
1. The CPU gives the first address of pin cycle, pin drive time, printing direction and pin
buffer and moves the C motor for the head to reach printing position. When the LFCK
signal is turned 0 → 1 → 0 or 1 → 0 → 1 (one of these will be selected according to
printing direction), printing starts.
2. Dot timing of the leading pin starts at the first edge of LFCK and dot timing of the next
successive pin starts at next edge. This dot timing refers to the time that it takes the
carriage head to move 1/720 inch.
3. DMA is operated according to the dot timing of each successive pin.
3.1 HRQ of BBG010 becomes "High".
3.2 When the CPU acknowledges hold (bus is released), XHAK becomes "High".
3.3 BBG010 transfers printing data to the printing buffer in BBG010 from 6 bytes of
DRAM.
3.4 After transferring data, BBG010 turns HRQ to "Low".
3.5 The CPU operates and XHAK becomes "High".
4. DMA repeats dot timing cycle until printing is completed.
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