Expansion Bus Host Port Operation
8-38
The step by step description of the events marked above the waveforms in
Figure 8–22 follows:
1) The XCS, XAS and XCNTL signals are low, low, and high respectively, in-
dicating XBISA register as the destination for the following transaction.
The XW/R is high specifying that a write access is taking place.
2) The ’C6202 begins driving the XRDY output in response to a transfer initi-
ated by the external host. A high XRDY indicates that the ’C6202 is not
ready.
3) The data is written to the XBISA register when the ’C202 asserts the XRDY
output low.
4) The XAS and XCNTL signals are both low (and XCS is low), indicating
XBD register as the destination for the following transaction. The XW/R is
high specifying that a write access is taking place.
5) The expansion bus master presents the valid data. The data is written to
the XBD register on the rising edge of the XCLKIN when XRDY is active-
low.
6) Same as 5.
7) The ‘C6202 is not ready to accept next data, which is indicated by XRDY
high.
8) Same as 5.
9) The expansion bus master indicates that the last write transaction is taking
place by asserting the XBLAST signal. The data is written to the XBD
register on the rising edge of the XCLKIN.