Z85233 Datasheet, PDF (174/317 Pages) Zilog, Inc. – The Zilog SCC Serial Communication Controller

Application Note
The Z180™ Interfaced with the SCC at MHZ
Table 8. Parameter Equations Worst Case (Without Delay Signals - No Wait State)
SCC
Parameters
TsA(RD)
TdA(DR)
TdRDf(DR)
TwRDI
TsA(WR)
TsDW(WR)
TwWRI
Z180
Equation
tcyc-tAD+tRDD1
3tcyc+tCHW+tcf-tAD-tDRS
2tcyc+tCHW+tcf-tRDD1-tDRS
2tcyc+tCHW+tcf-tDRS+tRDD2
tcyc-tAD+tWRD1
tWDS
tWRP
Value
30 min
245 min
160 min
185 min
30 min
15 min
210 min
Units
7
ns
ns
ns
ns
ns
ns
ns
Z180
Parameters
tDRS
Table 9. Parameter Equations
SCC
Equation
Address
3tcyc+tCHW-tAD-TdA(DR)
RD
2tcyc+tCHW-tRDD1-TdRD(DR)
Value
241 min
184 min
Units
ns
ns
I/O Read Cycle
These tables show that a delay of the falling edge of /RD
satisfies the SCC TsA(RD) timing requirement of 50 ns
min. The Z180 calculated value is 30 ns min for the worst
case. Also, Z180 timing specification tAH (Address Hold
time) is 10 ns min. The SCC timing parameters ThA(RD)
{Address to /RD High Hold} and ThCE(RD) {/CE to /RD
High Hold} are minimum at 0 ns. The rising edge of /RD is
early to guarantee these parameters when considering
address decoders and gate propagation delays.
I/O Write Cycle
Delay the falling edge of /WR to satisfy the SCC TsA(/WR)
timing requirement of 50 ns min. The Z180 calculates 30
ns min worst case. Further, the Z180 timing specifications
tAH (Address Hold time) and tWDH (/WR high to data hold
time) are both 10 ns min. The SCC timing parameters
ThA(WR) {Address to /WR High Hold}, ThCE(WR) {/CE to
/WR High Hold} and TdWR(W) {Write data to /WR High
hold} are a minimum of 0 ns. The rising edge of /WR is
early to guarantee these parameter requirements.
This circuit depicts logic for the I/O interface and the
Interrupt Acknowledge Interface for 10 MHz clock of
operation. Figure 13 is the I/O read/write timing chart
(discussions of timing considerations on the Interrupt
Acknowledge cycle and the circuit using EPLD occur
later).
UM010901-0601
6-39