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8xC196EA microcontroller user's manual.1998.pdf
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INTERFACING WITH EXTERNAL MEMORY

15.5.3 8-bit Bus Timings

Figure 15-11 shows idealized 8-bit timings for the microcontroller. One cycle is required for an 8-bit read or write. A 16-bit access requires two cycles. The first cycle accesses the lower byte, and the second cycle accesses the upper byte. Except for requiring an extra cycle to write the bytes separately, the timings are the same as on the 16-bit bus, and the comparison between the multiplexed and demultiplexed cases is also the same. The demultiplexed bus can accommodate slower memory devices than the multiplexed bus can.

15-27

8XC196EA USER’S MANUAL

 

 

 

Demultiplexed

 

 

 

 

CLKOUT

 

 

 

 

 

ALE

 

 

 

 

 

A20:0

 

Address Out

 

Address Out

 

AD15:8

 

High Address Out

High Address Out

RD#

 

 

 

 

 

AD7:0

 

 

Data In

 

Data In

(read)

 

 

 

 

 

WR#

 

 

 

 

 

AD7:0

 

Data Out

 

Data Out

(write)

 

 

 

 

 

Multiplexed

 

 

 

 

 

CLKOUT

 

 

 

 

 

ALE

 

 

 

 

 

A20:16

 

Extended Address Out

 

Extended Address Out

RD#

 

 

 

 

 

AD7:0

Data In

Low Address Out

Data In

Low Address Out

Data In

(read)

 

 

 

 

 

AD15:8

 

High Address Out

 

High Address Out

 

WR#

 

 

 

 

 

AD7:0

Data Out

Low Address Out

Data Out

Low Address Out

Data Out

(write)

 

 

 

 

 

AD15:8

 

High Address Out

High Address Out

 

 

 

 

 

A3286-01

Figure 15-12. Timings for Multiplexed and Demultiplexed 8-bit Buses

15-28

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