4501 datasheet(195/212 Pages) RENESAS

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3.3 List of precautions

3-26

Rev.2.01

Feb 07, 2005

4501 Group

APPENDIX

REJ09B0192-0201

3.3 List of precautions

3.3.1 Program counter

Make sure that the PCH does not specify after the last page of the built-in ROM.

3.3.2 Stack registers (SKS)

Stack registers (SKs) are eight identical registers, so that subroutines can be nested up to 8 levels.

However, one of stack registers is used respectively when using an interrupt service routine and when

executing a table reference instruction. Accordingly, be careful not to over the stack when performing these

operations together.

3.3.3 Notes on I/O port

(1)

Note when an I/O port is used as an input port

Set the output latch to “1” and input the port value before input. If the output latch is set to “0,” “L”

level can be input.

(2)

Noise and latch-up prevention

Connect an approximate 0.1

µF bypass capacitor directly to the VSS line and the VDD line with the

thickest possible wire at the shortest distance, and equalize its wiring in width and length.

The CNVSS pin is also used as the VPP pin (programming voltage = 12.5 V) at the One Time PROM

version.

Connect the CNVSS/VPP pin to VSS through an approximate 5 k

Ω resistor which is connected to the

CNVSS/VPP pin at the shortest distance.

(3)

Note on multifunction

• The input/output of D2, D3, P12 and P13 can be used even when C, K, CNTR (input) and INT are

selected.

• The input of P12 can be used even when CNTR (output) is selected.

• The input/output of P20 and P21 can be used even when AIN0 and AIN1 are selected.

(4)

Connection of unused pins

Table 3.3.1 shows the connections of unused pins.

(5)

SD, RD instructions

When the SD and RD instructions are used, do not set “01002” or more to register Y.

(6)

Analog input pins

When both analog input AIN0 and AIN1 and I/O port P2 function are used, note the following;

• Selection of analog input pins

Even when P20/AIN0 and P21/AIN1 are set to pins for analog input, they continue to function as port

P2 input/output. Accordingly, when any of them are used as I/O port and others are used as analog

input pins, make sure to set the outputs of pins that are set for analog input to “1.”

Also, the port input function of the pin functions as an analog input is undefined.

(7)

Notes on port P13/INT pin

When the bit 3 of register I1 is cleared, the RAM back-up mode is selected and the input of INT pin

is disabled, be careful about the following notes.

• When the key-on wakeup function of port P13 is not used (register K13 = “0”), clear bits 2 and 3

of register I1 before system enters to the RAM back-up mode.

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