2.1 CPU
28
Chapter 2: Hardware
(2) Register Bank Pointer (RP)
The RP register indicates the relationship between the general-purpose registers of the F2MC-16L core
and the address of internal RAM where these registers are located. The top memory address of the
register bank currently in use is indicated using the conversion formula [000180H + (RP) * 10H] (see
Figure 2.1.14). The RP register has 5-bit configuration and can take values from 00H to 1FH
corresponding to register banks having memory addresses 000180H to 00037FH. Note that addresses
within this range must be in internal RAM to be used as general-purpose registers. The RP register is
initialized to the value ‘00H’ by a reset.
The 8-bit immediate value can be transferred to the RP in the assumed form of instruction; only low-
order 5-bit data are actually used.
Fig. 2.1.14 Register Bank Pointer
(3) Interrupt Level Mask Register (ILM)
The ILM register has 3-bit configuration, and indicates the level of CPU interrupt masking. To be
received by the CPU, interrupt requests must have a stronger (higher) level than the setting of these
three bits. The strongest (highest) level is 0 and the weakest (lowest) level is 7 (see Table 2.1.4). Thus
for an interrupt to be received, it must be requested at a level with a smaller value than the current ILM
register value. When an interrupt is received, the value of its level is stored in the ILM register, and no
interrupts of equal or lower priority will then be received. Following a reset, all bits in the ILM register
are initialized to ‘0.’ When instructions are executed, the full 8-bit immediate data value can be
transferred to the ILM register, but only the upper three bits of the data are actually used.
Fig. 2.1.15 Interrupt Level Register
Table 2.1.4 Relative Strength of Levels in the Interrupt Level Mask Register (ILM)
ILM2
ILM1
ILM0
Level
value
Interrupt level enabled
0
Interrupt disabled
0
1
Level 0 only
0
1
0
2
Level 1 or stronger
0
1
3
Level 2 or stronger
1
0
4
Level 3 or stronger
1
0
1
5
Level 4 or stronger
1
0
6
Level 5 or stronger
1
7
Level 6 or stronger
B4 B3 B2 B1 B0
:RP
Initial value
0
ILM2
ILM1
ILM0
:ILM
Initial value
0