參數(shù)資料
型號(hào)： M37545GC-XXXGP
元件分類： 微控制器/微處理器
英文描述： 8-BIT, MROM, 4 MHz, MICROCONTROLLER, PQFP32
封裝： 7 X 7 MM, 0.80 MM PITCH, PLASTIC, LQFP-32
文件頁(yè)數(shù)： 53/63頁(yè)
文件大?。?/td> 774K
代理商： M37545GC-XXXGP
Rev.1.07
Mar 19, 2009
Page 57 of 60
REJ03B0140-0107
7545 Group
5. Read-modify-write instruction
Do not execute a read-modify-write instruction to the read
invalid address (SFR).
The read-modify-write instruction operates in the following
sequence: read one-byte of data from memory, modify the data,
write the data back to original memory. The following
instructions are classified as the read-modify-write instructions
in the 740 Family.
(1) Bit management 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
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 the read
invalid SFR.
<Reason>
When the read-modify-write instruction is executed to read
invalid SFR, the instru ction may cause the following
consequence: the instruction reads unspecified data from the area
due to the read invalid condition. Then the instruction modifies
this unspecified data and writes the data to the area. The result
will be random data written to the area or some unexpected
event.
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. Notes in stand-by state
In stand-by state*1 for low-power dissipation, do not make input
levels of an input port and an I/O port “undefined”.
Pull-up (connect the port to Vcc) or pull-down (connect the port
to Vss) these ports through a resistor.
When determining a resistance value, note the following points:
External circuit
Variation of output levels during the ordinary operation
When using a built-in pull-up resistor, note on varied current
values:
When setting as an input port : Fix its input level
When setting as an output port : Prevent current from flowing
out to external.
<Reason>
The output transistor becomes the OFF state, which causes the
ports to be the high-impedance state. Note that the level becomes
“undefined” depending on external circuits.
Accordingly, the potential which is input to the input buffer in a
microcomputer is unstable in the state that input levels of an
input port and an I/O port are “undefined”. This may cause
power source current.
*1 stand-by state : the stop mode by executing the STP
instruction
3. Modifying output data with bit managing instruction
When the port latch of an I/O port is modified with the bit
managing instruction*1, the value of the unspecified bit may be
changed.
<Reason>
I/O ports are set to input or output mode in bit units. Reading
from a port register or writing to it involves the following
operations.
Port in input mode
Read: Read the pin level.
Write: Write to the port latch.
Port in output mode
Read: Read the port latch or read the output from the
peripheral function (specifications differ depending on the
port).
Write: Write to the port latch. (The port latch value is output
from the pin.)
Since bit managing instructions*1 are read-modify-write
instructions,*2 using such an instruction on a port register causes
a read and write to be performed simultaneously on the bits other
than the one specified by the instruction.
When an unspecified bit is in input mode, its pin level is read and
that value is written to the port latch. If the previous value of the
port latch differs from the pin level, the port latch value is
changed.
If an unspecified bit is in output mode, the port latch is generally
read. However, for some ports the peripheral function output is
read, and the value is written to the port latch. In this case, if the
previous value of the port latch differs from the peripheral
function output, the port latch value is changed.
*1 Bit managing instructions: SEB and CLB instructions
*2 Read-modify-write instructions: Instructions that read
memory in byte units, modify the value, and then write the
result to the same location in memory in byte units
4. Direction register
The values of the port direction registers cannot be read.
That is, it is impossible to use the LDA instruction, memory
operation instruction when the T flag is “1”, addressing mode
using direction register values as qualifiers, and bit test
instructions such as BBC and BBS.
It is also impossible to use bit operation instructions such as CLB
and SEB and read-modify-write instructions of direction
registers for calculations such as ROR.
For setting direction registers, use the LDM instruction, STA
instruction, etc.
相關(guān)PDF資料
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