NEC PD754144 - Manual (Page 63)

CHAPTER 4 INTERNAL CPU FUNCTION
63 User’s Manual U10676EJ3V0UM
4.3 Program Memory (ROM) ··· 4096 × 8 bits
The program memory stores a program, interrupt vector table, the reference table of the GETI instruction, and table
data.
The program memory is addressed by the program counter. The table data can be referenced by using a table
reference instruction (MOVT).
Figure 4-3 shows address ranges in which execution can be branched by a branch or subroutine call instruction.
A relative branch instruction (BR $addr1 instruction) can branch execution to an address of [contents of PC –15 to
–1 or +2 to +16], regardless of the block boundary.
The address range of the program memory of each model is 0000H to 0FFFH, and among them, special functions
are assigned to the following addresses. All the addresses other than 0000H and 0001H can be used as normal
program memory addresses.
• Addresses 0000H and 0001H
These addresses store the start address from which program execution is to be started when the RESET signal
is asserted, and the vector table to which the set values of RBE and MBE are written. Program execution
can be reset and started from any address.
• Addresses 0002H to 000FH
These addresses store the start address from which program execution is to be started when a vector interrupt
occurs, and the vector table to which the set values of RBE and MBE are written. Interrupt servicing can be
started from any address.
• Addresses 0020H to 007FH
These addresses constitute a table area that can be referenced by the GETI instruction Note .
Note The GETI instruction implements any 2- or 3-byte instruction, or two 1-byte instructions with 1 byte. It is
used to decrease the number of program steps (refer to 11.1.1 GETI instruction).