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TC1796
System Units (Vol. 1 of 2)
LMB External Bus Unit
User’s Manual
13-71
V2.0, 2007-07
EBU, V2.0
13.9.5
Support for two Burst Flash Device Types
Support is provided for the use of two different Burst Flash configurations. This means,
two sets of burst access parameters (e.g. for different Burst Flash devices) can be
defined and stored in register EBU_BFCON, and depending on bit
EBU_BUSCONx.AGEN, one of these two parameter sets is selected. With AGEN = 0,
Burst Flash Type 0 access parameters are selected. With AGEN = 1, Burst Flash Type 1
access parameters are selected.
Bits DBA0, EBSE0, WAITFUNC0, FBBMSEL0, and bit field FETBLEN0 in the lower half
of register EBU_BFCON determine the characteristics for a Burst Flash Type 0 access.
Bits DBA1, EBSE1, WAITFUNC1, FBBMSEL1, and bit field FETBLEN1 in the upper half
of register EBU_BFCON determine the characteristics for a Burst Flash Type 1 access.
The control functions of bit field EXTCLOCK (burst clock frequency), bit BFCMSEL
(burst clock mode), bit FDBKEN (burst clock feedback control), and bit field DTALTNCY
(latency cycle control) are valid for both Burst Flash access types, independently of bit
AGEN.
13.9.6
BFCLKO Output
The EBU provides a clock signal BFCLKO (Burst Flash Clock Output) suitable for
clocking Burst Flash devices during burst read accesses. The BFCLKO signal can be
programmed to operate in one of two modes:
•
Ungated Mode: EBU_BFCON.BFCSEL = 0
•
Gated Mode: EBU_BFCON.BFCSEL = 1
In Ungated Mode, the BFCLKO clock signal is generated all the time, whether or not
burst cycles occur.
In Gated Mode, the BFCLKO clock signal is only active and generated during Burst Flash
access cycles. This is the default selection after reset. BFCLKO is at low level(0) in
inactive state. BFCLKO is also at low level during asynchronous read/writes of/to Burst
Flash devices. Operation in this mode provides power savings and ensures correct
asynchronous accesses of Burst Flash device(s).
Bit field EBU_BFCON.EXTCLOCK determines the frequency relation between LMBCLK
clock and of the BFCLKO output for both Burst Flash access types.
shows
all possible BFCLKO configurations that can be selected.