38D2 datasheet(119/136 Pages) RENESAS

119 / 136 page

Rev.3.02

Apr 10, 2008

Page 119 of 131

REJ03B0177-0302

38D2 Group

3. JMP Instruction

When using the JMP instruction (indirect addressing mode), do

not specify the address where “FF16” is allocated to the low-

order 8 bits as the operand.

4. Multiplication and Division Instructions

(1) The MUL and DIV instructions are not affected by the T and

D flags.

(2) Executing these instructions does not change the contents of

the processor status register.

5. Read-Modify-Write Instruction

Do not execute any read-modify-write instruction to the read

invalid (address) SFR.

The read-modify-write instruction reads 1-byte of data from

memory, modifies the data, and writes 1-byte the data to the

original memory.

In the 740 Family, the read-modify-write instructions are the

following:

(1) Bit handling instructions:

CLB, SEB

(2) Shift and rotate instructions:

ASL, LSR, ROL, ROR, RRF

(3) Add and subtract instructions:

DEC, INC

(4) Logical operation instructions (1’s complement):

COM

Although not the read-modify-write instructions, add and

subtract/logical operation instructions (ADC, SBC, AND, EOR,

and ORA) when T flag = “1” operate in the way as the read-

modify-write instruction. Do not execute them to the read invalid

SFR.

When the read-modify-write instruction is executed to the read

invalid SFR, the following may result:

As reading is invalid, the read value is undefined. The instruction

modifies this undefined value and writes it back, so the written

value will be indeterminate.

Notes on Peripheral Functions

Notes on I/O Ports

1. Use in Stand-By State

When using the MCU in stand-by state*1 for low-power

consumption, do not leave the input level of an I/O port

undefined. Be especially careful to the I/O ports for the N-

channel open-drain.

In this case, pull-up (connect to Vcc) or pull-down (connect to

Vss) these ports through a resistor.

When determining a resistance value, note the following:

• External circuit

• Variation in the output level during ordinary operation

When using a built-in pull-up resistor, note variations in current

values:

• When setting as an input port: Fix the input level

• When setting as an output port: Prevent current from

flowing out externally.

Even if a port is set to output by the direction register, when the

content of the port latch is “1”, the transistor becomes the OFF

state, which allows the port to be in the high-impedance state.

This may cause the level to be undefined depending on external

circuits.

As described above, if the input level of an I/O port is left

undefined, the power source current may flow because the

potential applied to the input buffer in the MCU will be unstable.

*1 Stand-by state: Stop mode by executing the STP instruction

Wait mode by executing the WIT instruction

2. Modifying Output Data with Bit Handling Instruction

When the port latch of an I/O port is modified with the bit

handling instruction*1, the value of an unspecified bit may

change.

I/O ports can be set to input mode or output mode in byte units.

When the port register is read or written, the following will be

operated:

• Port as input mode

Read: Read the pin level

Write: Write to the port latch

• Port as output mode

Read: Read the port latch or peripheral function output

(specifications vary depending on the port)

Write: Write to the port latch (output the content of the port

latch from the pin)

Meanwhile, the bit handling instructions are the read-modify-

write instructions*2. Executing the bit handling instruction to the

port register allows reading and writing a bit unspecified with the

instruction at the same time.

If an unspecified bit is set to input mode, the pin level is read and

the value is written to the port latch. At this time, if the original

content of the port latch and the pin level do not match, the

content of the port latch changes.

If an unspecified bit is set to output mode, the port latch is

normally read, but the peripheral function output is read in some

ports and the value is written to the port latch. At this time, if the

original content of the port latch and the peripheral function

output do not match, the content of the port latch changes.

*1 Bit handling instructions: CLB, SEB

*2 Read-modify-write instruction: Reads 1-byte of data from

memory, modifies the data, and writes 1-byte of the data to

the original memory.

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