MC7457RX1267LC Datasheet, PDF (25/71 Pages) Freescale Semiconductor, Inc – Microprocessor

Electrical and Thermal Characteristics
Table 11. Sample Points Calculation Parameters
Parameter
Symbol
Max
Unit Notes
Delay from processor clock to internal_L3_CLK
t_AC
3/4
t_{L3_CLK}
1
Delay from internal_L3_CLK to L3_CLK[n] output pins
t_CO
3
ns
2
Delay from L3_ECHO_CLK[n] to receive latch
t_ECI
3
ns
3
Notes:
1. This specification describes a logical offset between the internal clock edge used to launch the L3 address and control signals
(this clock edge is phase-aligned with the processor clock edge) and the internal clock edge used to launch the L3_CLK[n]
signals. With proper board routing, this offset ensures that the L3_CLK[n] edge will arrive at the SRAM within a valid address
window and provide adequate setup and hold time. This offset is reflected in the L3 bus interface AC timing specifications,
but must also be separately accounted for in the calculation of sample points and, thus, is specified here.
2. This specification is the delay from a rising or falling edge on the internal_L3_CLK signal to the corresponding rising or falling
edge at the L3CLK[n] pins.
3. This specification is the delay from a rising or falling edge of L3_ECHO_CLK[n] to data valid and ready to be sampled from
the FIFO.
5.2.4.1 Effects of L3OHCR Settings on L3 Bus AC Specifications
The AC timing of the L3 interface can be adjusted using the L3 Output Hold Control Register (L3OCHR).
Each field controls the timing for a group of signals. The AC timing specifications presented herein
represent the AC timing when the register contains the default value of 0x0000_0000. Incrementing a field
delays the associated signals, increasing the output valid time and hold time of the affected signals. In the
special case of delaying an L3_CLK signal, the net effect is to decrease the output valid and output hold
times of all signals being latched relative to that clock signal. The amount of delay added is summarized
in Table 12. Note that these settings affect output timing parameters only and do not impact input timing
parameters of the L3 bus in any way.
Table 12. Effect of L3OHCR Settings on L3 Bus AC Timing
At recommended operating conditions. See Table 4.
Field Name¹
L3AOH
Affected Signals
L3_ADDR[18:0],
L3_CNTL[0:1]
Value
0b00
0b01
0b10
0b11
Output Valid Time
Output Hold Time
Parameter
Symbol ²
Change ³
Parameter
Symbol ²
Change ³
t_L3CHOV
0
+50
+100
+150
t_L3CHOX
0
+50
+100
+150
Unit
ps
Notes
4
MPC7457 RISC Microprocessor Hardware Specifications, Rev. 8
Freescale Semiconductor
25