Expansion Bus Host Port Operation
8-27
Expansion Bus
Table 8–16. Expansion Bus Pin Description (Synchronous Host Port Mode) (Continued)
Signal
Symbol
Signal Function
Signal
Name
Signal
Count
Signal
Type
XD[31:0]
I/O/Z
32
Address/
data bus
Data
XBLAST
I/O/Z
1
Burst last
Signal driven by the current expansion bus master to
indicate the last transfer in a bus access. Input polarity
selected at boot. Output polarity is always active low.
XAS
I/O/Z
1
Address
Strobe
Indicates a valid address and the start of a new bus access.
Asserted for the first clock of a bus access.
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
XBE[3:0]/
XA[5:2]
I/O/Z
4
Byte
enables
During host-port accesses these signals operate as
XBE[3:0].
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]
XW/R
I/O/Z
1
Read/write
Write/read enable
Polarity of this signal is configured during boot.
XRDY
I/O/Z
1
Ready out
Ready in
Active(low) during host-port access. XRDY is an input when
the ’C6202 owns the bus. When the ’C6202 does not own
the bus, XRDY is not driven until a request is made to the
’C6202.
XBOFF
I
1
Bus
Back-Off
When asserted, suspends the current access and the
’C6202 releases ownership of the expansion bus.
XWAIT
O
1
Wait
Ready output for master accesses