80C196KB USER’S GUIDE
Case 1. Meeting Thvcl
270651 – 82
Case 2. Asserting HOLD Asynchronously
270651 – 83
Figure 15-12. HOLD Applied Asynchronously
DISABLING HOLD REQUESTS
Clearing the HLDEN bit (WSR.7), can disable HOLD
requests when consecutive memory cycles are required.
Clearing the HDLEN bit, however, does not cause the
80C196KB to take over the bus immediately. The
80C196KB waits for the current HOLD request to fin-
ish. Then it disables the bus hold feature, causing any
new requests to be ignored until the HLDEN bit is set
again. Since there is a delay from the time the code for
clearing this bit is fetched to the time it is actually exe-
cuted, the code that clears HLDEN needs to be a few
instructions ahead of the block that needs to be protect-
ed from HOLD requests.
The safest way is to add a JBC instruction to check the
status of the HLDA pin after the code that clears the
HLDEN bit. Figure 15-13 is an example of code that
prevents the part from executing a new instruction until
both current HOLD requests are serviced and the hold
feature is disabled.
15.5 AC Timing Explanations
Figure 15-14 shows the timing of the ADDR/DATA
bus and control signals. Refer to the latest data sheet
for the AC timings to make sure your system meets
specifications. The major timing specifications are ex-
plained in Figure 15-15.
DI
; disable interrupts
ANDB WSR,
#
OEFH
; disable hold request
WAIT:
JBC PORT1, 6, WAIT; Check the HLDA pin
#
; If set, execute
#
; protected instructions
#
ORB WSR,
#
80h
; enable HOLD requests
EI
; enable interrupts
NOTE:
Interrupts should be disabled to prevent code interruption
Figure 15-13. HOLD code
78
数控原理与维修
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Содержание 80C196KB Series
Страница 1: ...November 1990 80C196KB User s Guide Order Number 270651 003 http www agreenleaf cn...
Страница 59: ...80C196KB USER S GUIDE Figure 11 7 Ideal A D Characteristic 270651 37 55 http www agreenleaf cn...
Страница 60: ...80C196KB USER S GUIDE Figure 11 8 Actual and Ideal Characteristics 270651 38 56 http www agreenleaf cn...
Страница 61: ...80C196KB USER S GUIDE Figure 11 9 Terminal Based Characteristic 270651 39 57 http www agreenleaf cn...
Страница 70: ...80C196KB USER S GUIDE Figure 13 5 Reset Sequence 80C196KB Reset Sequence 270651 45 66 http www agreenleaf cn...
Страница 83: ...80C196KB USER S GUIDE 270651 80 Figure 15 14 AC Timing Diagrams 79 http www agreenleaf cn...
Страница 84: ...80C196KB USER S GUIDE 270651 81 270651 84 Figure 15 14 AC Timing Diagrams Continued 80 http www agreenleaf cn...