INTERFACING WITH EXTERNAL MEMORY

XTAL1

 

 

 

 

CLKOUT

 

 

 

 

ALE

 

 

 

 

BUSWIDTH

 

 

 

 

AD15:8

 

Address Out

 

Address Out

AD7:0

Address

Low data in

Address

High data in

(read)

Out

+1 Out

 

 

RD#

 

 

 

 

INST

 

 

 

 

AD7:0

Address

Low data out

Address

High data out

(write)

Out

+1 Out

 

 

WR#

 

 

 

 

The CLKOUT pin is available only on the 8XC196MC, MD.

A3164-01

Figure 15-7. Timings for 8-bit Buses

15.4 WAIT STATES (READY CONTROL)

An external device can use the READY input to lengthen an external bus cycle. When an external address is placed on the bus, the external device can pull the READY signal low to indicate it is not ready. In response, the microcontroller inserts wait states to lengthen the bus cycle until the

external device raises the READY signal. Each wait state adds one state time (2TXTAL1) to the bus cycle.

After reset and until CCB1 is fetched, the bus controller always inserts three wait states into bus cycles. Then, until P5.6 has been configured to operate as the READY signal, the internal ready control bits (IRC2:0) control the wait states.

15-17

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Intel 8XC196MC, 8XC196MD, 8XC196MH manual Wait States Ready Control, Timings for 8-bit Buses