參數(shù)資料
型號： M37549G2-XXXFP
元件分類： 微控制器/微處理器
英文描述： 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PDSO24
封裝： 5.30 X 10.10 MM, 0.80 MM PITCH, PLASTIC, SSOP-24
文件頁數(shù)： 75/86頁
文件大小： 1375K
代理商： M37549G2-XXXFP
Rev.2.02
Mar 31, 2009
Page 75 of 81
REJ03B0202-0202
7549 Group
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.
<Reason>
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. Pull-up control register
When using each port which built in pull-up resistor as an output
port, the pull-up control bit of corresponding port becomes
invalid, and pull-up resistor is not connected.
<Reason>
Pull-up control is effective only when each direction register is
set to the input mode.
2. 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.
<Reason>
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
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