Expansion Bus Host Port Operation
8-41
Expansion Bus
8.5.3
Asynchronous Host Port Mode
This mode is slave only, it uses a 32-bit data path, and it is similar to the HPI
on the ‘C6201. The asynchronous host port mode is used to interface to asyn-
chronous microprocessor buses.
A list of the signals when the expansion bus operates in the asynchronous host
port mode is given in Table 8–17.
Table 8–17. Expansion Bus Pin Description (Asynchronous Host Port Mode)
Signal
Symbol
Signal
Type
Signal
Count
Signal Name
Signal Function
XCS
I
1
Chip Select
Selects the ‘C6202 as a target of an external master.
XD[31:0]
I/O/Z
32
Data Bus
XBE[3:0]
I
4
Byte Enables
Functionality of these signals is the same as on the
‘C6201 HPI (during a read XBE do not matter). During
a write:
BE3 byte enable 3– XD[31:24]
BE2 byte enable 2– XD[23:16]
BE1 byte enable 1– XD[15:8]
BE0 byte enable 0– XD[7:0]
XCNTL
I
1
Control Signal
This signal selects between XBD and XBISA register.
XCNTL=0, access is made to the XBD register
XCNTL=1, access is made to the XBISA register
XW/R
I
1
Read/Write
Polarity of this signal is configured during boot.
XRDY
O/Z
1
Ready Out
Ready signal indicates normally not ready condition.
This signal is always driven in asynch host mode when
the ’C6202 does not own the bus.
The XCNTL signal selects which internal register the host is accessing. The
state of this pin selects if access is made to the expansion bus internal slave
address (XBISA) register or, expansion bus data (XBD) register.