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8XC196NP, 80C196NU USER’S MANUAL
13-30
Figure 13-15. READY Timing Diagram — Demultiplexed Mode (80C196NU)
13.7 BUS-HOLD PROTOCOL
The 8XC196Nx supports a bus-hold protocol that allows external devices to gain control of the
address/data bus. The protocol uses three signals, all of which are port 2 special functions:
HOLD#/P2.5 (bus-hold request), HLDA#/P2.6 (bus-hold acknowledge), and BREQ#/P2.3 (bus
request). When an external device wants to use the 8XC196Nx bus, it asserts the HOLD# signal.
HOLD# is sampled while CLKOUT is low. The 8XC196Nx responds by releasing the bus and
asserting HLDA#. During this hold time, the address/data bus floats, and signals CSx#, ALE,
RD#, WR#/WRL#, BHE#/WRH#, and INST are weakly held in their inactive states. Figure
13-16 shows the timing for bus-hold protocol, and Table 13-12 on page 13-31 lists the timing pa-
rameters and their definitions. Refer to the datasheet for timing parameter values.
T0014-02
T
CHYX
(max)
T
WLWH
+ 2t
T
AVYV
T
LHLH
+ 2t
T
RLRH
+ 2t
T
AVDV
+ 2t
T
RLDV
+ 2t
T
QVWH
+ 2t
Data Valid
Data Valid
CLKOUT
READY
ALE
RD#
AD15:0
WR#
AD15:0
BHE#, INST
A19:16
CS
x
#
T
CHYX
(min)
(read)
(write)