Expansion Bus I/O Port Operation
8-14
Table 8–8. Synch FIFO Pin Description
Signal
Signal Function
Signal
Name
(I/O/Z)
Signal Purpose
R/W Mode
Read Mode
XFCLK
O
FIFO clock output
Programmable to either 1/2, 1/4, 1/6, or 1/8 of the CPU clock
frequency. If CPU clock = 250 MHz, then XFCLK = 125, 62.5, 41.7 or
31.25 MHz. The XFCLK continues to clock even when the DSP
releases ownership of the XBUS.
XD[31:0]
I/O/Z
Data
Data lines
XCEx
O
FIFO read
enable/write
enable/chip Select
Active for both read and write
transactions. They should be
logically OR-ed with output control
signals externally to create
dedicated controls for a FIFO. Also
can be used directly as FIFO write
enable signal for a single write FIFO
per XCE space.
Acts as read enable
signal(XCE3 only)
XWE
O
FIFO write enable
Write-enable signal for FIFO. Must
be logically OR-ed with
corresponding XCE signal to
ensure that only one FIFO is
addressed at a time.
XRE
O
FIFO read enable
Read-enable signal for FIFO. Must
be logically OR-ed with
corresponding XCE signal to
ensure that only one FIFO is
addressed at a time.
XOE
O
FIFO output
enable
Shared output enable signal. Must
be logically OR-ed with
corresponding XCE signal to
ensure that only one FIFO is
addressed at a time.
Dedicated output enable signal
in XCE3 if FIFO read mode is
selected.
If selected, this signal
is disabled for all other modes.
XBE[3:0]/
XA[5:2]
O/Z
Expansion bus
address
Operate as XA[5:2]. Can be de-
coded to specify up to 16 different
addresses, enabling interface with
glue to 16 Read FIFOs and 16 Write
FIFOs in a single XCE space.