CHAPTER 3 CPU ARCHITECTURE
3.1.1 Internal program memory space
The internal program memory space stores programs and table data. This space is usually addressed by the
program counter (PC).
The µPD789426, 789436, 789446, and 789456 Subseries provide internal ROM (or flash memory) with the
following capacity for each product.
Table 3-1. Internal ROM Capacity
Part Number
Internal ROM
Structure
Capacity
µPD789425, 789435,
Mask ROM
12288 × 8 bits
789445, 789455
µPD789426, 789436,
16384 × 8 bits
16384 × 8 bits
789446, 789456
µPD78F9436, 78F9456
Flash memory
The following areas are allocated to the internal program memory space.
(1) Vector table area
The 34-byte area of addresses 0000H to 0021H is reserved as a vector table area. This area stores
program start addresses to be used when branching by the RESET input or an interrupt request generation.
Of a 16-bit program address, the lower 8 bits are stored in an even address, and the higher 8 bits are stored
in an odd address.
Table 3-2. Vector Table
Vector Table Address
0000H
Interrupt Request
RESET input
INTWDT
Vector Table Address
0014H
Interrupt Request
INTWTI
0004H
0016H
INTTM90
INTTM50
INTTM60
INTAD0
0006H
INTP0
0018H
0008H
INTP1
001AH
000AH
INTP2
001CH
000CH
INTP3
001EH
INTWT
000EH
INTSR20/INTCSI20
INTST20
0020H
INTKR00
0012H
(2) CALLT instruction table area
The subroutine entry address of a 1-byte call instruction (CALLT) can be stored in the 64-byte area of
addresses 0040H to 007FH.
User’s Manual U15075EJ1V0UM00
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