M37517F8HP Datasheet, PDF (56/98 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

7517 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 addressing mode which uses the value of a direction regis-
ter 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 SRDY1 signal, set the transmit
enable bit, the receive enable bit, and the SRDY1 output enable bit
to “1”.
Serial I/O1 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 transmis-
sion is completed.
When an external clock is used as synchronous clock in serial I/
O1 or serial I/O2, write transmission data to the transmit buffer
register or serial I/O2 register while the 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 or WIT instruction during an A/D conver-
sion.
Instruction Execution Time
The instruction execution time is obtained by multiplying the fre-
quency 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 frequency of the internal clock φ is half of the XIN frequency in
high-speed mode.
NOTES ON USAGE
Handling of 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 µF 0.1µF 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 unstable operation.
Rev.1.01 Aug 02, 2004 page 56 of 96