NEC UPD789026 Series, User Manual

Page: 46 / 213

CHAPTER 3 CPU ARCHITECTURE
User's Manual U11919EJ3V0UM00
46
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
µ
PD789026 Subseries provides the internal ROMs (or flash memory) containing the following capacities on
each product.
Table 3-1. Internal ROM Capacity
Internal ROM Part Number
Structure Capacity
µ
PD789022 4,096
×
8 bits
µ
PD789024 8,192
×
8 bits
µ
PD789025 12,288
×
8 bits
µ
PD789026
Mask ROM
16,384
×
8 bits
µ
PD78F9026A Flash memory 16,384
×
8 bits
The following areas are allocated to the internal program memory space:
(1) Vector table area
A 44-byte area of addresses 0000H to 002BH 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 low-order 8 bits are stored in an even address, and the high-order 8 bits are stored
in an odd address.
Table 3-2. Vector Table
Vector Table Address Interrupt Request Vector Table Address Interrupt Request
0000H RESET input 000CH INTSR/INTCSI0
0004H INTWDT 000EH INTST
0006H INTP0 0010H INTTM0
0008H INTP1 0014H INTTM2
000AH INTP2 002AH INTKR
(2) CALLT instruction table area
In a 64-byte area of addresses 0040H to 007FH, the subroutine entry address of a 1-byte call instruction
(CALLT) can be stored.
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