Electrical and Thermal Characteristics
Table 9. Processor Bus AC Timing Specifications (continued)
1
At recommended operating conditions. See Table 4.
All Speed Grades
2
Parameter
Symbol
Unit
Notes
Min
Max
SYSCLK to ARTRY/SHD0/SHD1 high impedance after
precharge
t
—
2
t
3, 5,
6, 7
KHARPZ
SYSCLK
Notes:
1. All input specifications are measured from the midpoint of the signal in question to the midpoint of the rising edge of the input
SYSCLK. All output specifications are measured from the midpoint of the rising edge of SYSCLK to the midpoint of the signal
in question. All output timings assume a purely resistive 50-Ω load (see Figure 4). Input and output timings are measured at
the pin; time-of-flight delays must be added for trace lengths, vias, and connectors in the system.
2. The symbology used for timing specifications herein follows the pattern of t
for inputs and
(signal)(state)(reference)(state)
t
for outputs. For example, t
symbolizes the time input signals (I) reach the valid state (V)
(reference)(state)(signal)(state)
IVKH
relative to the SYSCLK reference (K) going to the high (H) state or input setup time. And t
symbolizes the time from
KHOV
SYSCLK(K) going high (H) until outputs (O) are valid (V) or output valid time. Input hold time can be read as the time that the
input signal (I) went invalid (X) with respect to the rising clock edge (KH) (note the position of the reference and its state for
inputs) and output hold time can be read as the time from the rising edge (KH) until the output went invalid (OX).
3. t
is the period of the external clock (SYSCLK) in ns. The numbers given in the table must be multiplied by the period of
sysclk
SYSCLK to compute the actual time duration (in ns) of the parameter in question.
4. According to the bus protocol, TS is driven only by the currently active bus master. It is asserted low then precharged high
before returning to high impedance as shown in Figure 6. The nominal precharge width for TS is 0.5 × t
, that is, less
SYSCLK
than the minimum t
period, to ensure that another master asserting TS on the following clock will not contend with the
SYSCLK
precharge. Output valid and output hold timing is tested for the signal asserted. Output valid time is tested for precharge. The
high-impedance behavior is guaranteed by design.
5. Guaranteed by design and not tested.
6. According to the bus protocol, ARTRY can be driven by multiple bus masters through the clock period immediately following
AACK. Bus contention is not an issue because any master asserting ARTRY will be driving it low. Any master asserting it low
in the first clock following AACK will then go to high impedance for one clock before precharging it high during the second
cycle after the assertion of AACK. The nominal precharge width for ARTRY is 1.0 t
; that is, it should be high
SYSCLK
impedance as shown in Figure 6 before the first opportunity for another master to assert ARTRY. Output valid and output
hold timing is tested for the signal asserted. The high-impedance behavior is guaranteed by design.
7. According to the MPX bus protocol, SHD0 and SHD1 can be driven by multiple bus masters beginning the cycle of TS. Timing
is the same as ARTRY, that is, the signal is high impedance for a fraction of a cycle, then negated for up to an entire cycle
(crossing a bus cycle boundary) before being three-stated again. The nominal precharge width for SHD0 and SHD1 is 1.0
t
. The edges of the precharge vary depending on the programmed ratio of core-to-bus (PLL configurations).
SYSCLK
8. BMODE[0:1] and BVSEL are mode select inputs and are sampled before and after HRESET negation. These paramenters
represent the input setup and hold times for each sample. These values are guaranteed by design and not tested. These
inputs must remain stable after the second sample. See Figure 5 for sample timing.
Figure 4 provides the AC test load for the MPC7455.
Output
OV /2
DD
Z = 50 Ω
0
R = 50 Ω
L
Figure 4. AC Test Load
MPC7455 RISC Microprocessor Hardware Specifications, Rev. 4.1
18
Freescale Semiconductor
FREESCALE [ Freescale ]
