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14-13
INTERFACING WITH EXTERNAL MEMORY
14.4.2 16-bit Bus Timings
When the device is configured to operate in the 16-bit bus-width mode, lines AD15:0 form a 16-
bit multiplexed address/data bus. Figure 14-6 shows an idealized timing diagram for the external
read and write cycles. (Comprehensive timing specifications are shown in Figure 14-25).
The rising edge of the address latch enable (ALE) indicates that the device is driving an address
onto the bus (A19:16 and AD15:0). The device presents a valid address before ALE falls. The
ALE signal is used to strobe a transparent latch (such as a 74AC373), which captures the address
from AD15:0 and holds it while the bus controller puts data onto AD15:0.
For 16-bit read cycles, the bus controller floats the bus and then drives RD# low so that it can
receive data. The external memory must put data (Data In) onto the bus before the rising edge of
RD#. The data sheet specifies the maximum time the memory device has to output valid data after
RD# is asserted. When INST is asserted, it indicates that the read operation is an instruction fetch.
For 16-bit write cycles, the bus controller drives WR# low, then puts data onto the bus. The rising
edge of WR# signifies that data is valid. At this time, the external system must latch the data.
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 36: ...2 Architectural Overview...
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Страница 50: ...3 Programming Considerations...
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Страница 66: ...4 Memory Partitions...
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Страница 104: ...5 Standard and PTS Interrupts...
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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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