參數(shù)資料
型號(hào)： M37512F8HP
元件分類： 微控制器/微處理器
英文描述： 8-BIT, FLASH, 4 MHz, MICROCONTROLLER, PQFP48
封裝： 7 X 7 MM, 0.50 MM PITCH, PLASTIC, LQFP-48
文件頁(yè)數(shù)： 73/89頁(yè)
文件大?。?/td> 877K
代理商： M37512F8HP
Feb 18, 2005
page 73 of 85
REJ03B0122-0101
7512 Group
NOTES ON PROGRAMMING
Processor Status Register
The contents of the processor status register (PS) after a reset are
undefined, except for the interrupt disable flag (I) which is “1.” Af-
ter a reset, initialize flags which affect program execution. In
particular, it is essential to initialize the index X mode (T) and the
decimal mode (D) flags because of their effect on calculations.
Interrupts
The contents of the interrupt request bits do not change immedi-
ately after they have been written. After writing to an interrupt
request register, execute at least one instruction before perform-
ing a BBC or BBS instruction.
Decimal Calculations
To calculate in decimal notation, set the decimal mode flag (D)
to “1”, then execute an ADC or SBC instruction. After executing
an ADC or SBC instruction, execute at least one instruction be-
fore executing a SEC, CLC, or CLD instruction.
In decimal mode, the values of the negative (N), overflow (V),
and zero (Z) flags are invalid.
Timers
If a value n (between 0 and 255) is written to a timer latch, the fre-
quency division ratio is 1/(n+1).
Multiplication and Division Instructions
The index X mode (T) and the decimal mode (D) flags do not af-
fect the MUL and DIV instruction.
The execution of these instructions does not change the con-
tents of the processor status register.
Ports
The contents of the port direction registers cannot be read. The
following cannot be used:
The data transfer instruction (LDA, etc.)
The operation instruction when the index X mode flag (T) is “1”
The instruction with the addressing mode which uses the value
of a direction register as an index
The bit-test instruction (BBC or BBS, etc.) to a direction register
The read-modify-write instructions (ROR, CLB, or SEB, etc.) to
a direction register.
Use instructions such as LDM and STA, etc., to set the port direc-
tion registers.
Serial interface
In clock synchronous serial I/O, if the receive side is using an ex-
ternal clock and it is to output the SRDY signal, set the transmit
enable bit, the receive enable bit, and the SRDY output enable bit
to “1.”
Serial I/O continues to output the final bit from the TXD pin after
transmission is completed. SOUT2 pin for serial I/O2 goes to high
impedance after transfer is completed.
When in serial I/Os 1 and 3 (clock-synchronous mode) or in serial
I/O2, an external clock is used as synchronous clock, write trans-
mission data to the transmit buffer register or serial I/O2 register,
during transfer clock is “H.”
A/D Converter
The comparator uses capacitive coupling amplifier whose charge
will be lost if the clock frequency is too low.
Therefore, make sure that f(XIN) is at least on 500 kHz during an
A/D conversion.
Do not execute the STP instruction during an A/D conversion.
Instruction Execution Time
The instruction execution time is obtained by multiplying the pe-
riod of the internal clock
φ by the number of cycles needed to
execute an instruction.
The number of cycles required to execute an instruction is shown
in the list of machine instructions.
The period of the internal clock
φ is double of the XIN period in
high-speed mode.
NOTES ON USAGE
Handling of Power Source Pins
In order to avoid a latch-up occurrence, connect a capacitor suit-
able for high frequencies as bypass capacitor between power
source pin (VCC pin) and GND pin (VSS pin), and between power
source pin (VCC pin) and analog power source input pin (AVSS
pin). Besides, connect the capacitor to as close as possible. For
bypass capacitor which should not be located too far from the pins
to be connected, a ceramic capacitor of 0.01
F–0.1 F is recom-
mended.
Power Source Voltage
When the power source voltage value of a microcomputer is less
than the value which is indicated as the recommended operating
conditions, the microcomputer does not operate normally and may
perform unstable operation. In a system where the power source
voltage drops slowly when the power source voltage drops or the
power supply is turned off, reset a microcomputer when the power
source voltage is less than the recommended operating conditions
and design a system not to cause errors to the system by this un-
stable operation.
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