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TC1796
System Units (Vol. 1 of 2)
LMB External Bus Unit
User’s Manual
13-44
V2.0, 2007-07
EBU, V2.0
The equivalent control capability is available for bit fields EBU_EMUBAP.WAITRDC and
EBU_BUSAPx.WAITWRC, which are multiplied by EBU_EMUBC.CMULT.
Additionally, when accessing asynchronous devices, a Command Phase can also be
extended externally using the WAIT signal when the region being accessed is
programmed for external command delay control via bit EBU_BUSCONx.WAIT or
EBU_EMUBC.WAIT.
The Command Phase is further subdivided into:
•
CPi (= internally-programmed Command Phase)
•
CPe (= externally-prolonged Command Phase, i.e. prolonged by the assertion of the
WAIT signal).
At the start of the Command Phase, the EBU:
•
Asserts the appropriate control signal RD or RD/WR low according to the access type
(read or write),
•
Issues the data to be written on the data bus D[31:0] (in the case of a write cycle),
•
Asserts the appropriate BCx low (in the case where BCx is programmed to be
asserted with the RD or RD/WR signals).
At the end of the Command Phase during an asynchronous access, the EBU:
•
Returns the appropriate control signal RD or RD/WR high according to the type of
access type (read or write),
•
Latches the data from the data bus D[31:0] (in the case of a read cycle),
•
Returns the appropriate BCx high (in the case where BCx is programmed to be
asserted with the RD or RD/WR signals).
The EBU takes no action at the end of the Command Phase during an access to a Burst
Flash device (i.e. no signals are changed or sampled).
During accesses to Burst Flash devices, the Command Phase is always extended by
zero or more LMBCLK cycles to ensure that the end of the Command Phase coincides
with a positive edge of the appropriate BFCLKO (Burst Flash clock output) signal.
Cycle Type
Number of Command Phase Cycles
Read Cycle
= WAITRDC
×
CMULT
Write Cycle
= WAITWRC
×
CMULT