User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 11: Generic/Boot Bus Page
365
In the fixed mode, the cycle time is:
ale ale cs 1 + idle_cycle
In the acknowledgement mode the minimum cycle time is:
ale ale cs rdy 1 + idle_cycle
Table 248: Generic Bus Timing Parameters
Name
Range
(cycle = 10ns)
IO_CS[0]
Reset
Description
ale_width
1 - 7 cycles
4
Width of the address latch enable pulse. This signal is asserted for this
number of cycles to indicate the start of the cycle, the address and byte
enables are output at the same time this signal asserts and remain stable
after IO_ALE deasserts (i.e. IO_ALE is suitable for use as the latch input of
a flow through latch, or the clock input of a falling-edge clocked flipflop).
ale_to_cs
1 - 3 cycles
2
Delay from IO_ALE being deasserted until assertion of the IO_CS_L line
for the region addressed.
cs_width
1 - 31 cycles
24
The width of the chip select assertion in fixed cycle mode. In
acknowledgement mode the IO_RDY line will not be sampled until this
number of cycles have passed, but the chip select remains asserted until
the IO_RDY signal has been asserted and rdoe_to_cs cycles
have passed.
rdy_smple
0 - 7 cycles
1
In acknowledgement mode this is the number of cycles from IO_RDY
asserting to IO_WR_L or IO_OE_L deasserting (and data being latched in
a read access). The chip select remains asserted oe_to_cs additional
cycles.
idle_cycle
1 - 15 cycles
6
The number of cycles that the bus should be idle before the next IO_ALE.
Note that the cycle does not end until one cycle after the IO_CS_L line has
deasserted.
ale_to_wr
1 - 7 cycles
7
The number of cycles from IO_ALE deassertion to IO_WR_L assertion in a
write cycle.
wr_width
1 - 15 cycles
7
In fixed mode this is the number of cycles that IO_WR_L is asserted in a
write cycle. In acknowledgement mode this value is ignored and the
IO_WR_L strobe deassserts rdy_smple cycles after the acknowledgement.
cs_to_oe
0 - 3 cycles
0
The number of cycles from IO_CS_L assertion to IO_OE_L assertion is a
read cycle.
oe_to_cs
0 - 3 cycles
0
In fixed timing mode this sets the number of cycles before IO_CS_L
deassertion that IO_OE_L deasserts in a read cycle.
In acknowledgement mode this sets the number of cycles between the
strobe (IO_WR_L or IO_OE_L) deasserting and IO_CS_L deasserting.
io_timeout
(in
io_ext_cfg
)
1 - 255 us
8
The number of microseconds to wait for the device to assert IO_RDY in
acknowledgment mode before terminating the access and signalling a
timeout bus error.
If this parameter is set to zero the access will never be terminated with a
timeout, so will hang if an acknowledgement is never provided.
burst_width
0 - 3 cycles
2’’b0
Sets the number of cycles gap between a transfer in a burst transaction.
The gap is two cycles larger than the value set in this field.