BCM1250/BCM1125/BCM1125H
User Manual
10/21/02
B r o a d c o m C o r p o r a t i o n
Page
366
Section 11: Generic/Boot Bus
Document
1250_1125-UM100CB-R
The reference point for the IO_WR_L write strobe is the deassertion of IO_ALE, it is the responsibility of
software to ensure that the assertion timing (and width in fixed cycles) places the strobe within the cycle timing.
It is required that
ale_to_wr >= ale_to_cs
(cs ale_to_cs) >= (wr ale_to_wr)
Similarly, in acknowledgement mode the IO_OE_L and IO_WR_L timing is expected to assert the pulses
before the IO_RDY line is checked. It is required that
cs_width >= cs_to_oe
cs_width >= (ale_to_wr - ale_to_cs)
Failure to meet these assumptions will result in UNDEFINED behavior.
F
IXED
C
YCLE
R
EAD
A
CCESS
Figure 74: Fixed Cycle Read Access
A fixed read cycle has the simplest timing. The address is put out at the start of the cycle along with IO_ALE.
In the non-multiplexed version the address remains stable until the end of the cycle and the data lines are high
impedance until the device drives them. In the multiplexed form the address stays valid until IO_CS_L asserts
and the bus is turned around for data transfer. The read strobe IO_OE_L is asserted with a delay (which may
be zero) from IO_CS_L and will deassert a fixed number of cycles (which may be zero) before IO_CS_L. The
write strobe IO_WR_L remains deasserted for the entire cycle.
cs_width
ale_to_cs
idle_cycle
ale_width
1 cycle
Address
Data
Address
Data
Non Muxed
Muxed
Parity
clk100
io_ale
io_ad[23:0]
io_ad[31:24]
io_ad[31:0]
io_adp[3:0]
io_cs_l[n]
io_oe_l
io_wr_l
io_rdy
cs_to_oe
oe_to_cs