7643 datasheet(301/424 Pages) RENESAS

301 / 424 page

Rev.2.00

Aug 28, 2006

page 180 of 202

7643 Group

REJ09B0133-0200

APPLICATION

2.8 External device connection

The HOLD function is used for systems that consist of external circuits that access MCU buses without

use of the CPU (Central Processing Unit). The HOLD function is used to generate the timing in which

the MCU will relinquish the bus from the CPU to the external circuits. To use the HOLD function, set

the HOLD function enable bit (b5 of CPMB) to “1”. This can be enabled in the memory expansion mode

and microprocessor mode.

When “L” level is input to the HOLD pin, the MCU goes to the HOLD state and remains so while the

pin is at “L”. When the MCU relinquishes use of the bus, “L” level is output from the HLDA pin. The MCU

puts ports P0 and P1 (address buses) and port P2 (data bus) to tri-state outputs and holds the RD pin

(P37) and WR pin (P36) “H” level. This will prevent incorrect operations of external devices.

Though the clock supply to the CPU halts in HOLD state, the internal peripheral clocks and

φOUT (P34)

continues to be supplied.

When “H” level is input to the HOLD pin,“H” level is output from the HLDA pin and the MCU can use

address buses, data bus, signals RD and WR to access to external devices.

Figure 2.8.7 shows the Hold function timing diagram.

2.8.5 HOLD function

Fig. 2.8.7 Hold function timing diagram

XIN

RD, WR

ADDROUT

DATAIN/OUT

HOLD

HLDA

φ OUT

tsu(HOLD-

φ)

th(

φ-HOLD)

td(

φ-HLDAL)

td(

φ-HLDAH)

Note: This diagram assumes

φ = XIN/2.

7643 Datasheet(PDF) 301 Page - Renesas Technology Corp