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2.4.2
Program Counter (PC)
This 24-bit counter indicates the address of the next instruction the CPU will execute. The length
of all CPU instructions is 2 bytes (one word), so the least significant PC bit is ignored. (When an
instruction is fetched, the least significant PC bit is regarded as 0).
2.4.3
Extended Control Register (EXR)
EXR is an 8-bit register that manipulates the LDC, STC, ANDC, ORC, and XORC instructions.
When these instructions, except for the STC instruction, are executed, all interrupts including NMI
will be masked for three states after execution is completed.
Bit
Bit Name
7
T
6 to 3
2
I2
1
I1
0
I0
SP (ER7)
Figure 2.8 Stack
Initial
Value
R/W
Description
0
R/W
Trace Bit
When this bit is set to 1, a trace exception is generated
each time an instruction is executed. When this bit is
cleared to 0, instructions are executed in sequence.
All 1
Reserved
These bits are always read as 1.
1
R/W
These bits designate the interrupt mask level (0 to 7).
For details, refer to section 5, Interrupt Controller.
1
R/W
1
R/W
Free area
Stack area
Rev. 1.00 Mar. 12, 2008 Page 33 of 1178
REJ09B0403-0100
Section 2 CPU
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