
ADSP-21992
Rev. A
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Page 35 of 60
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August 2007
External Port Write Cycle Timing
The external port lets systems extend read/write accesses in
three ways: wait states, ACK input, and combined wait states
and ACK. To add waits with ACK, the DSP must see ACK low
at the rising edge of EMI clock. ACK low causes the DSP to wait,
and the DSP requires two EMI clock cycles after ACK goes high
to finish the access. For more information, see the External Port
chapter in the ADSP-2199x DSP Hardware Reference.
Table 20. External Port Write Cycle Timing
Parameter
Min
Max
Unit
Timing Requirements1, 2
tAKW
ACK Strobe Pulse Width
12.5
ns
tDWSAK
ACK Delay from XMS Low
0.5tEMICLK – 1
ns
Switching Characteristics
tCSWS
Chip Select Asserted to WR Asserted Delay
0.5tEMICLK – 4
ns
tAWS
Address Valid to WR Setup and Delay
0.5tEMICLK – 3
ns
tWSCS
WR Deasserted to Chip Select Deasserted
0.5tEMICLK – 4
ns
tWSA
WR Deasserted to Address Invalid
0.5tEMICLK – 3
ns
tWW
WR Strobe Pulse Width
tEMICLK–2 + W
3
ns
tCDA
WR to Data Enable Access Delay
0
ns
tCDD
WR to Data Disable Access Delay
0.5tEMICLK – 3
0.5tEMICLK + 4
ns
tDSW
Data Valid to WR Deasserted Setup
tEMICLK + 1 + W
3
tEMICLK + 7 + W
3
ns
tDHW
WR Deasserted to Data Invalid Hold Time; E_WHC4, 5
3.4
ns
tDHW
WR Deasserted to Data Invalid Hold Time; E_WHC4, 6
tEMICLK+3.4
ns
tWWR
WR Deasserted to WR, RD Asserted
tHCLK
ns
1 tEMICLK is the external memory interface clock period. tHCLK is the peripheral clock period.
2 These are timing parameters that are based on worst-case operating conditions.
3 W = (number of wait states specified in wait register)
tEMICLK.
4 Write hold cycle memory select control registers (MS 3 CTL).
5 Write wait state count (E_WHC) = 0
6 Write wait state count (E_WHC) = 1