7733 Datasheet, PDF (344/940 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER

CONNECTING EXTERNAL DEVICES
12.4 Hold function
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.
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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
Oscillation
Operating
φCPU
Stopped at “L”
A0 to A7, A8/D8 to A15/D15, ^Floating
__ ____
A16/D0 to A23/D7, R/W, BHE
State
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HLDA, ALE
P42/φ1
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.
P43 to P47, P5 to P8
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Retains the same state in which HOLD was accepted.
Timers A and B, Serial I/O, Operating
A-D converter
Watchdog timer
Stopped
Clock φ1 output selection bit^*1: Bit 7 at address 5E16
Signal output disable selection bit^*2: Bit 6 at address 6C16
7733 Group User’s Manual
12–19