System Integration Module (SIM60)
MOTOROLA
MC68360 USER’S MANUAL
6-25
The keyed write uses the MBAR enable (MBARE) register at address $0003FF08 and the
MBARE pin. Both the newly located MBAR and the MBARE are located in the CPU address
space FC = 111.
With multiple QUICCs configured in slave mode, the following keyed write is used to enable
the MBAR programming: the user writes the MBAR select bit of MBARE with a 1 while the
MBARE pin is a logic zero. Once this is accomplished, the MBAR may be written at its new
location (using the standard MBAR writing techniques). Once MBAR is written (in particular,
the low-order byte of MBAR), then the MBAR select bit in MBARE is cleared, and further
accesses to MBAR are impossible until the keyed write technique is used again. There is no
time limit imposed between the keyed write and the MBAR write; however, once the keyed
write for a particular QUICC slave has occurred, the MBAR of that slave should be written
before performing another keyed write to another QUICC slave.
The keyed write may be performed gluelessly to multiple QUICC slaves in the following way.
Connect (in hardware) the MBARE pin of QUICC slave #1 to bit zero of the data bus(D0).
Connect the MBARE pin of QUICC slave #2 to D1, etc. Then perform the following opera-
tions in software:
1. Write the MBARE of QUICC slave #1 at $0003FF08 with value $FFFFFFFE. This sets
the MBAR select bit (bit 31) and places a low voltage on only the MBARE pin of QUICC
slave #1.
2. Now the MBAR of QUICC slave #1 can be accessed at $0003FF04 and written using
normal MBAR writing procedures.
3. Write the MBARE of QUICC slave #2 with the value $FFFFFFFD.
4. Now the MBAR of QUICC slave #2 can be written.
This technique will work for up to 31 QUICC slaves in the system, using no glue or parallel
I/O pins.
6.8.2 Global Chip Select (CS0) in Slave Mode
When the QUICC is in slave mode, the user may choose whether to enable the global chip-
select operation of CS0. (The global chip select is used for boot ROMs and is described in
6.10 Memory Controller.) The global chip select can be either enabled or disabled by the
configuration on the CONFIG pins during power-up reset and system reset (RESETH
asserted). When the global chip select function is disabled, CS0 can still be enabled later
and used as a normal chip select, if desired.
6.8.3 Bus Clear in Slave Mode
The bus clear out (BCLRO) pin can be selected to signify to the external logic that the DRAM
refresh controller, IDMA channels, or SDMA channels are requesting the bus. However, in
slave mode, the BCLRO pin may become the RAS2DD double drive pin, and a new pin
called bus clear in (BCLRI) is defined (at another location in the pinout). BCLRI indicates to
that QUICC that a request is being made for the QUICC to release the system bus. The EBI
will then clear all internal bus masters with an arbitration ID smaller than the programmed
value of the bus clear in ID (BCLRIID) in the MCR.