INTERFACING WITH EXTERNAL MEMORY

 

Table 15-5. READY Signal Timing Definitions (Continued)

 

 

Symbol

Definition

 

 

††

READY Hold after ALE Low

TLLYX

 

Minimum time the level of the READY signal must be valid after ALE falls. If the maximum

 

value is exceeded, additional wait states will occur.

 

 

††

ALE Low to READY Setup

TLLYV

 

Maximum time the external device has to deassert READY after ALE falls.

 

 

TQVWH

Data Valid to WR# High

 

Time between data being valid on the bus and the microcontroller deasserting WR#.

 

 

TRLDV

RD# Low to Input Data Valid

 

Maximum time the memory system has to output valid data after the microcontroller asserts

 

RD#.

 

 

TRLRH

RD# Low to RD# High

 

RD# pulse width.

 

 

TWLWH

WR# Low to WR# High

 

WR# pulse width.

 

 

TXTAL1

1/FXTAL1

 

All AC timings are referenced to TXTAL1.

This specification applies to the 8XC196MC, MD microcontrollers only.

††This specification applies to the 8XC196MH microcontroller only.

15.5 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 15-6 lists the four bus-control modes and shows the CCR0.3 and CCR0.2 settings for each.

.

Table 15-6. Bus-control Modes

Bus-control Mode

Bus-control Signals

CCR0.3

CCR0.2

(ALE)

(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

 

 

 

 

15-21

Page 336
Image 336
Intel 8XC196MD, 8XC196MH, 8XC196MC BUS-CONTROL Modes, Bus-control Modes, Bus-control Mode Bus-control Signals CCR0.3 CCR0.2