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9-1
CHAPTER 9
INTERFACING WITH EXTERNAL MEMORY
The 87C196CB’s external memory interface is similar to that of the 8XC196NT. However, the
87C196CB supports only two of the bus timing modes, modes 3 and 0. In addition, the 100-pin
87C196CB has four additional address pins (A23:20).
9.1 ADDRESS PINS
The 100-pin 87C196CB has 24 available address pins, A23:16 and AD15:0. The A23:20 timings
are identical to those of A19:16. During the CCB fetch, the 100-pin 87C196CB strongly drives
0FFH on A23:16. The 84-pin 87C196CB strongly drives 0FH on A19:16, as does the
8XC196NT.
9.2 BUS TIMING MODES
The 87C196CB implements only modes 3 and 0. Table 9-1 and Figure 9-1 compare the timings
of these two modes. Figure 9-2 illustrates the CCB1 register, which selects the mode.
Table 9-1. Modes 0 and 3 Timing Comparisons
Mode
Timing Specifications
†
T
CLLH
T
AVLL
T
AVDV
T
RLRH
T
RHDZ
T
RLDV
Mode 3 0 1t 3t 1t 1t 1t
Mode 0 0 1t 5t 3t 1t 3t
†
These are ideal timing values for purposes of comparison only. They do not include internal
device delays. Consult the datasheet for current device specifications.