HD64336901G Renesas Technology, HD64336901G Datasheet - Page 86

• Manufacturer Part Number: HD64336901G
• Description: (HD64xxx Series) 16-BIT MICROCONTROLLER
• Manufacturer: Renesas Technology

3.5
3.5.1
If an interrupt is accepted after a reset and before the stack pointer (SP) is initialized, the PC and
CCR will not be saved correctly, leading to a program crash. To prevent this, all interrupt requests,
including NMI, are disabled immediately after a reset. Since the first instruction of a program is
always executed immediately after the reset state ends, make sure that this instruction initializes
the stack pointer (example: MOV.W #xx: 16, SP).
3.5.2
When word data is accessed, the least significant bit of the address is regarded as 0. Access to the
stack always takes place in word size, so the stack pointer (SP: R7) should never indicate an odd
address. Use PUSH Rn (MOV.W Rn, @–SP) or POP Rn (MOV.W @SP+, Rn) to save or restore
register values.
3.5.3
When a port mode register is rewritten to switch the functions of external interrupt pins, IRQ3,
IRQ0, and WKP5, the interrupt request flag may be set to 1.
When switching a pin function, mask the interrupt before setting the bit in the port mode register.
After accessing the port mode register, execute at least one instruction (e.g., NOP), then clear the
interrupt request flag from 1 to 0.
Figure 3.4 shows a port mode register setting and interrupt request flag clearing procedure.
Rev. 1.00, 11/03, page 58 of 376
Figure 3.4 Port Mode Register Setting and Interrupt Request Flag Clearing Procedure
Interrupts after Reset
Notes on Rewriting Port Mode Registers
Usage Notes
Notes on Stack Area Use
Clear interrupt request flag to 0
Set port mode register bit
Execute NOP instruction
CCR I bit
CCR I bit
1
0
Interrupts masked. (Another possibility
is to disable the relevant interrupt in
interrupt enable register 1.)
After setting the port mode register bit,
first execute at least one instruction
(e.g., NOP), then clear the interrupt
request flag to 0
Interrupt mask cleared