Panasonic JB-3300 Technical Manual page 404

HOST INTERFACE
The NDC 841 and NDC 843 are for the host interface section. The NDC 841,
when combined with the NDC 840 and other parts, is designed to facilitate
configuration of a disk controller for the SASi interface.
The NDC 843 can be used to convert the timing of the SASi interface (with
NDC 84l-configured disk controller) to ensure compatibility with the IBM-
PC/XT's bus timing.
To write commands or data from the host computer, the commands or data are
first set in the NDC 843's internal register and then are transferred to
RAM by the NDC 840's DMA mode.
Similarly, to read status data or other data, the data are first read from
RAM and set in the NDC 841's internal register, and then are read into the
host computer.
Time Chart of Principal Operations
a. Controller selection (322H)
Select the controller before starting execution. When BUSY becomes
active, terminate the selection.
BUSY
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