m3819 Renesas Electronics Corporation., m3819 Datasheet - Page 65

• Manufacturer Part Number: m3819
• Description: Mitsubishi 8-bit Single-chip Microcomputer 740 Family / 38000 Series
• Manufacturer: Renesas Electronics Corporation.

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 performing
a BBC or BBS instruction.
Decimal Calculations
• To calculate in decimal notation, set the decimal mode flag (D)
• In decimal mode, the values of the negative (N), overflow (V),
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-
• The execution of these instructions does not change the con-
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 register
• the bit-test instruction (BBC or BBS, etc.) to a direction register
• the read-modify-write instructions (ROR, CLB, or SEB, etc.) to a
Use instructions such as LDM and STA, etc., to set the port direc-
tion registers.
to “1”, then execute an ADC or SBC instruction. Only the ADC
and SBC instructions yield proper decimal results. After execut-
ing an ADC or SBC instruction, execute at least one instruction
before executing a SEC, CLC, or CLD instruction.
and zero (Z) flag are invalid.
The carry flag can be used to indicate whether a carry or borrow
has occurred. Initialize the carry flag before each calculation.
Clear the carry flag before an ADC and set the flag before an
SBC.
fect the MUL and DIV instruction.
tents of the processor status register.
as an index
direction register.
Serial I/O
When using an external clock, input “H” to the external clock input
pin and clear the serial I/O interrupt request bit before executing
serial I/O transfer and serial I/O automatic transfer.
When using the internal clock, set the synchronous clock to inter-
nal clock, then clear the serial I/O interrupt request bit before
executing a serial I/O transfer and serial I/O automatic transfer.
A-D Converter
The comparator uses internal capacitors whose charge will be lost
if the clock frequency is too low.
Make sure that f(X
sion.
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
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
At the STP Instruction Release
At the STP instruction release, all bits of the timer 12 mode regis-
ter are cleared.
The X
to “1” (high drive) in order to start oscillating.
COUT
is half of the X
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
drivability selection bit (the CPU mode register) is set
IN
) is 500 kHz or more during an A-D conver-
MITSUBISHI MICROCOMPUTERS
IN
or X
CIN
by the number of cycles needed to
frequency.
3819 Group
51