7733 datasheet(344/940 Pages) RENESAS

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CONNECTING EXTERNAL DEVICES

7733 Group User’s Manual

12–19

12.4 Hold function

When an external circuit which accesses the bus without using the central processing unit (CPU), for

example DMA, is used, it is necessary to generate a timing for transferring the right to use of the bus from

the CPU to the external circuit. The hold function is used to generate this timing.

_____

By applying “L” level to pin HOLD in the memory expansion or microprocessor mode, the microcomputer

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enters the hold state. While pin HOLD’s level is “L,” this state is retained. Table 12.4.1 lists the microcomputer’s

state in the hold state.

In the hold state, oscillation of the oscillator does not stop. Therefore, the internal peripheral devices can

operate even in the hold state. (Note that the watchdog timer stops.)

Table 12.4.1 Microcomputer’s state in hold state

Item

State

Operating

Stopped at “L”

Floating

Oscillation

φCPU

A0 to A7, A8/D8 to A15/D15,

____

A16/D0 to A23/D7, R/W, BHE

Outputs “L” level.

In the memory expansion mode

s When the clock

φ1 output selection bit*1 = “1”

Outputs clock

φ1.

s When the clock

φ1 output selection bit = “0”

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Retains the same state in which HOLD was accepted.

In the microprocessor mode

s When the signal output disable selection bit*2= “1”

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Retains the same state in which HOLD was accepted.

s When the signal output disable selection bit = “0”

Outputs clock

φ1.

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Retains the same state in which HOLD was accepted.

Operating

Stopped

Clock

φ1 output selection bit*1: Bit 7 at address 5E16

Signal output disable selection bit*2: Bit 6 at address 6C16

_____

HLDA

, ALE

P42/

φ1

P43 to P47, P5 to P8

Timers A and B, Serial I/O,

A-D converter

Watchdog timer

12.4 Hold function

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