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Bus Control Signals
follow the handshake protocol described in this section. The maximum number of bits
accepted or provided during a bus transfer is defined as the port width.
The MPC533 has non-multiplexed address and data buses. Control signals indicate the
beginning and type of the cycle, as well as the address space and size of the transfer. The
selected device then controls the length of the cycle with the signal(s) used to terminate the
cycle. A strobe signal for the address lines indicates the validity of the address.
The MPC533 bus is synchronous with a synchronous support. The bus and control input
signals must be timed to setup and hold times relative to the rising edge of the clock. Bus
cycles can be completed in two clock cycles.
For all inputs, the MPC533 latches the level of the input during a sample window around
the rising edge of the clock signal. This window is illustrated in Figure 9-1, where t
and
su
t
are the input setup and hold times, respectively. To ensure that an input signal is
ho
recognized on a specific rising edge of the clock, that input must be stable during the sample
window. If an input makes a transition during the window time period, the level recognized
by the MPC533 is not predictable; however, the MPC533 always resolves the latched level
to either a logic high or low before using it. In addition to meeting input setup and hold
times for deterministic operation, all input signals must obey the protocols described in this
section.
t
ho
t
su
Clock
Signal
Sample
Window
Figure 9-1. Input Sample Window
9.3
Bus Control Signals
The MPC533 initiates a bus cycle by driving the address, size, address type, cycle type, and
read/write outputs. At the beginning of a bus cycle, TSIZ[0:1] are driven with the address
type signals. TSIZ0 and TSIZ1 indicate the number of bytes remaining to be transferred
during an operand cycle (consisting of one or more bus cycles). These signals are valid at
the rising edge of the clock in which the transfer start (TS) signal is asserted.
9-2
MPC533 Reference Manual
MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
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