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Computer Group Literature Center Web Site
Falcon ECC Memory Controller Chipset
3
designer to be able to implement general-purpose status/control signals
with this external set. Refer to
for a description of
this register set.
CSR Accesses
An important part of the operation of a Falcon pair is that the value written
to the internal control registers and SRAM in each of the two chips must
be the same at all times. In order to facilitate this, writes to the pair itself
are restricted to the upper Falcon only. When software writes to the upper
Falcon, hardware in the two chips shifts this same value into the lower
Falcon before the cycle completion is acknowledged. The shifting is done
in holding registers such that the actual update of the control register
happens on the same CLOCK cycle in both chips. Writes to the upper
Falcon can be single-byte or 4-byte. Writes to the lower Falcon are
ignored.
This duplicating of writes from upper to lower applies to the Falcon’s
internal registers and SRAM only. No duplication is performed for writes
to DRAM, ROM/Flash, or the External Register set.
Programming Model
CSR Architecture
The CSR (control and status register set) consists of the chip’s internal
register set, its test SRAM, and its external register set. The base address
of the CSR is hard coded to the address $FEF80000 (or $FEF90000 if the
SIO pin is low at reset).
Accesses to the CSR are mapped differently depending on whether they
are reads or writes. For reads, CSR data read on the upper half of the data
bus comes from the upper Falcon while CSR data read on the lower half of
the data bus comes from the lower Falcon. (See
.)