Fujitsu F2MC-8L MB89620 Series Hardware Manual page 64

n Features of General-purpose Registers
General-purpose registers have the following features:
• RAM can be accessed at high-speed using short instructions (general-purpose register
addressing).
• Registers are grouped in blocks in the form of register banks. This simplifies the process of
saving register contents and dividing registers by function.
Dedicated register banks can be permanently assigned for each interrupt processing or vector
call (CALLV #0 to #7) processing routine by general-purpose register. For example, register
bank 4 interrupt 2.
For example, a particular interrupt processing routine only uses a particular register bank which
cannot be written to unintentionally by other routines. The interrupt processing routine only
needs to specify its dedicated register bank at the start of the routine to effectively save the
general-purpose registers in use prior to the interrupt. Therefore, saving the general-purpose
registers to the stack or other memory location is not necessary. This allows high-speed
interrupt handling while maintaining simplicity.
Also, as an alternative to saving general-purpose registers in subroutine calls, register banks
can be used to create reentrant programs (programs that do not use fixed addresses and can
be entered more than once) usually made by the index register (IX).
Check: If an interrupt processing routine changes the register bank pointer (RP), ensure that the program
does not also change the interrupt level bits in the condition code register (CCR: IL1, IL0) when
specifying the register bank.
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CHAPTER 3 CPU