MC7457RX1267LC Datasheet, PDF (26/71 Pages) Freescale Semiconductor, Inc – Microprocessor

Electrical and Thermal Characteristics
Table 12. Effect of L3OHCR Settings on L3 Bus AC Timing (continued)
At recommended operating conditions. See Table 4.
Field Name¹
Affected Signals
Value
Output Valid Time
Output Hold Time
Parameter
Symbol ²
Change ³
Parameter
Symbol ²
Change ³
Unit
Notes
L3CLKn_OH
All signals latched by 0b000 t_L3CHOV,
0
t_L3CHOX,
0
ps
4
SRAM connected to
L3_CLKn
0b001
t_L3CHDV,
t_L3CLDV
– 50
t_L3CHDX,
t_L3CLDX
– 50
5
0b010
– 100
– 100
5
0b011
– 150
– 150
5
0b100
– 200
– 200
5
0b101
– 250
– 250
5
0b110
– 300
– 300
5
0b111
– 350
– 350
5
L3DOHn
L3_DATA[n:n+7],
0b000 t_L3CHDV,
0
t_L3CHDX,
0
ps
4
L3_DP[n/8]
0b001
t_L3CLDV
+ 50
t_L3CLDX
+ 50
0b010
+ 100
+ 100
0b011
+ 150
+ 150
0b100
+ 200
+ 200
0b101
+ 250
+ 250
0b111
+ 300
+ 300
0b111
+ 350
+ 350
Notes:
1. See the MPC7450 RISC Microprocessor Family User’s Manual for specific information regarding L3OHCR.
2. See Table 13 and Table 14 for more information.
3. Approximate delay verified by simulation; not tested or characterized.
4. Default value.
5. Increasing values of L3CLKn_OH delay the L3_CLKn signal, effectively decreasing the output valid and output hold times of
all signals latched relative to that clock signal by the SRAM; see Figure 9 and Figure 11.
5.2.4.2 L3 Bus AC Specifications for DDR MSUG2 SRAMs
When using DDR MSUG2 SRAMs at the L3 interface, the parts should be connected as shown in Figure 9.
Outputs from the MPC7457 are actually launched on the edges of an internal clock phase-aligned to
SYSCLK (adjusted for core and L3 frequency divisors). L3_CLK0 and L3_CLK1 are this internal clock
output with 90° phase delay, so outputs are shown synchronous to L3_CLK0 and L3_CLK1. Output valid
times are typically negative when referenced to L3_CLKn because the data is launched one-quarter period
before L3_CLKn to provide adequate setup time at the SRAM after the delay-matched address, control,
data, and L3_CLKn signals have propagated across the printed-wiring board.
Inputs to the MPC7457 are source-synchronous with the CQ clock generated by the DDR MSUG2
SRAMs. These CQ clocks are received on the L3_ECHO_CLKn inputs of the MPC7457. An internal
circuit delays the incoming L3_ECHO_CLKn signal such that it is positioned within the valid data
MPC7457 RISC Microprocessor Hardware Specifications, Rev. 8
26
Freescale Semiconductor