MPC555CME Freescale Semiconductor, MPC555CME Datasheet - Page 303

• Manufacturer Part Number: MPC555CME
• Description: KIT EVALUATION FOR MPC555
• Manufacturer: Freescale Semiconductor
• Type: Microcontrollerr

Specifications of MPC555CME

• Contents: Module Board, Installation Guide, Power Supply, Cable, Software and more
• Processor To Be Evaluated: MPC555
• Data Bus Width: 32 bit
• Interface Type: RS-232
• For Use With/related Products: MPC555
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

9.5 Bus Operations
MPC555
USER’S MANUAL
This section provides a functional description of the system bus, the signals that con-
trol it, and the bus cycles provided for data transfer operations. It also describes the
error conditions, bus arbitration, and reset operation.
The MPC555 / MPC556 generates a system clock output (CLKOUT). This output sets
the frequency of operation for the bus interface directly. Internally, the MPC555 /
MPC556 uses a phase-lock loop (PLL) circuit to generate a master clock for all of the
CPU circuitry (including the bus interface) which is phase-locked to the CLKOUT out-
put signal.
All signals for the MPC555 / MPC556 bus interface are specified with respect to the
rising edge of the external CLKOUT and are guaranteed to be sampled as inputs or
changed as outputs with respect to that edge. Since the same clock edge is referenced
for driving or sampling the bus signals, the possibility of clock skew could exist be-
tween various modules in a system due to routing or the use of multiple clock lines. It
Signal Name
Bus request
Bus grant
Bus busy
/
MPC556
BR
BG
BB
Table 9-1 MPC555 / MPC556 SIU Signals (Continued)
Pins
1
1
1
EXTERNAL BUS INTERFACE
Active
Low
Low
Low
Rev. 15 October 2000
ARBITRATION
I/O
O
O
O
I
I
I
When the internal arbiter is enabled, BR assertion in-
dicates that an external master is requesting the bus.
Driven by the MPC555 / MPC556 when the internal
arbiter is disabled and the chip is not parked.
When the internal arbiter is enabled, the MPC555 /
MPC556 asserts this signal to indicate that an exter-
nal master may assume ownership of the bus and be-
gin a bus transaction. The BG signal should be
qualified by the master requesting the bus in order to
ensure it is the bus owner:
Qualified bus grant = BG & ~ BB
When the internal arbiter is disabled, BG is sampled
and properly qualified by the MPC555 / MPC556
when an external bus transaction is to be executed by
the chip.
When the internal arbiter is enabled, the MPC555 /
MPC556 asserts this signal to indicate that it is the
current owner of the bus.
When the internal arbiter is disabled, the MPC555 /
MPC556 asserts this signal after the external arbiter
has granted the ownership of the bus to the chip and
it is ready to start the transaction.
When the internal arbiter is enabled, the MPC555 /
MPC556 samples this signal to get indication of when
the external master ended its bus tenure (BB negat-
ed).
When the internal arbiter is disabled, the BB is sam-
pled to properly qualify the BG line when an external
bus transaction is to be executed by the chip.
Description
MOTOROLA
9-7