Fujitsu F2MC-8FX Hardware Manual page 54

CHAPTER 5 CPU
Features of General-purpose Registers
The general-purpose registers have the following features:
• High-speed access to RAM using short instructions (general-purpose register addressing).
• Blocks of register banks facilitating data backup and division by function unit.
General-purpose register banks can be allocated exclusively for specific interrupt service routines or vector
call (CALLV #0 to #7) processing routines. An example is always using the fourth register bank for the
second interrupt.
Only specifying a dedicated register bank at the beginning of an interrupt service routine automatically
saves the general-purpose registers before the interrupt. This eliminates the need for pushing general-
purpose register data onto the stack, allowing the CPU to accept interrupts at high speed.
Notes:
• When coding an interrupt service routine, be careful not to change the value of the interrupt level bits
(CCR: IL1, IL0) in the condition code register when specifying the register bank by updating the register
bank pointer (RP) in that routine. Perform the programming by using either of them.
• Read the interrupt level bits and save their value before writing to the RP.
• Directly write to the RP mirror address "0078
40
" to update the RP.
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