MMC2107 - Freescale Semiconductor

Chip Select Module
Freescale Semiconductor, Inc.
CSEN — Chip Select Enable Bit
The CSEN bit enables the chip select logic. When the chip select
function is disabled, the CSx signal is negated high.
1 = Chip select function enabled
0 = Chip select function disabled
20.7 Functional Description
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Freescale Semiconductor, I
Each chip select can provide a chip enable signal for an external device
and assert the internal bus cycle termination signal.
Setting the CSEN bit in CSCR enables the chip select to provide an
external chip enable.
Setting both the CSEN and TAEN bits in CSCR enables the chip select
to generate the internal bus cycle termination signal.
Both the chip select pin assertion and the bus cycle termination function
depend on an initial address/option match for activation. During the
matching process, the fixed base address of each chip select is
compared to the corresponding address for the bus cycle to determine
whether an address match has occurred. This match is further qualified
by comparing the internal read/write indication and access type with the
programmed values in CSCR of each chip select. When the address and
option information match the current cycle, the chip select is activated. If
no chip select matches the bus cycle information for the current access,
the chip select logic does not respond in any way.
Only one chip select can be active for a given bus cycle. The
configuration of the active chip select, determined by the wait state
(WS/WWS) field, the port size (PS) field, and the write enable (WE) field,
is used for the access.
NOTE:
WWS and WS are valid only if the TAEN bit is 1 for the active chip select.
When no chip select pin is available, the active chip select can still
terminate the bus cycle. If both the CSEN and TAEN bits are 1 and the
address/options match the chip select configuration, then the chip select
logic asserts the internal termination signal; the bus cycle terminates
after the programmed number of wait states. If the external TA or TEA
Technical Data MMC2107 – Rev. 2.0
530 Chip Select Module MOTOROLA
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