7641 datasheet(257/385 Pages) RENESAS

257 / 385 page

Rev.2.00

Aug 28, 2006

page 126 of 148

7641 Group

REJ09B0336-0200

APPLICATION

2.10 External devices 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 2.10.7 shows the Hold function timing diagram.

2.10.5 HOLD function

Fig. 2.10.7 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.

7641 Datasheet(PDF) 257 Page - Renesas Technology Corp