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14-23
INTERFACING WITH EXTERNAL MEMORY
If the device is reset while in hold, bus contention can occur. For example, a CPU-only device
(80C196NT) would try to fetch the chip configuration byte from external memory after RESET#
was brought high. Bus contention would occur because both the external device and the micro
controller would attempt to access memory. One solution is to use the RESET# signal as the sys-
tem reset; then all bus masters (including the device) are reset at once. Chapter 12, “Minimum
Hardware Considerations,” shows system reset circuit examples.
14.7 BUS-CONTROL MODES
The ALE and WR bits (CCR0.3 and CCR0.2) define which bus-control signals will be generated
during external read and write cycles. Table 14-6 lists the four bus-control modes and shows the
CCR0.3 and CCR0.2 settings for each.
.
14.7.1 Standard Bus-control Mode
In the standard bus-control mode, the device generates the standard bus-control signals: ALE,
RD#, WR#, and BHE# (see Figure 14-10). ALE is asserted while the address is driven, and it can
be used to latch the address externally. RD# is asserted for every external memory read, and WR#
is asserted for every external memory write. When asserted, BHE# selects the bank of memory
that is addressed by the high byte of the data bus.
Table 14-6. Bus-control Mode
Bus-control Mode
Bus-control Signals
CCR0.3
(ALE)
CCR0.2
(WR)
Standard Bus-control Mode
ALE, RD#, WR#, BHE#
1
1
Write Strobe Mode
ALE, RD#, WRL#, WRH#
1
0
Address Valid Strobe Mode
ADV#, RD#, WR#, BHE#
0
1
Address Valid with Write Strobe Mode
ADV#, RD#, WRL#, WRH#
0
0
Содержание 8XC196NT
Страница 1: ...8XC196NT Microcontroller User s Manual...
Страница 2: ...8XC196NT Microcontroller User s Manual June 1995 Order Number 272317 003...
Страница 22: ...1 Guide to This Manual...
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Страница 35: ......
Страница 36: ...2 Architectural Overview...
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Страница 49: ......
Страница 50: ...3 Programming Considerations...
Страница 51: ......
Страница 66: ...4 Memory Partitions...
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Страница 104: ...5 Standard and PTS Interrupts...
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Страница 147: ......
Страница 148: ...6 I O Ports...
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Страница 176: ...7 Serial I O SIO Port...
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Страница 194: ...8 Synchronous Serial I O SSIO Port...
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Страница 212: ...9 Slave Port...
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Страница 232: ...10 Event Processor Array EPA...
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Страница 270: ...11 Analog to digital Converter...
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Страница 292: ...12 Minimum Hardware Considerations...
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Страница 306: ...13 Special Operating Modes...
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Страница 318: ...14 Interfacing with External Memory...
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Страница 362: ...15 Programming the Nonvolatile Memory...
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Страница 408: ...A Instruction Set Reference...
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Страница 476: ...B Signal Descriptions...
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Страница 494: ...C Registers...
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Страница 566: ...Glossary...
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Страница 580: ...Index...
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