MITSUBISHI
ELECTRIC
14
MITSUBISHI MICROCOMPUTERS
4250 Group
SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER
Fig. 10 ROM map of M34250M2
Fig. 11 Page 1 (addresses 0080
16
to 00FF
16
) structure
Fig. 12 RAM map
A part of page 1 (addresses 0080
16
to 00FF
16
) is reserved for
interrupt addresses (Figure 11). When an interrupt occurs, the
address (interrupt address) corresponding to each interrupt is
set in the program counter, and the instruction at the interrupt
address is executed. When using an interrupt service routine,
write the instruction generating the branch to that routine at an
interrupt address.
Page 2 (addresses 0100
16
to 017F
16
) is the special page for
subroutine calls. Subroutines written in this page can be called
from any page with the 1-word instruction (BM). Subroutines
extending from page 2 to another page can also be called with
the BM instruction when it starts on page 2.
ROM pattern (bits 7 to 0) of all addresses can be used as data
areas with the TABP p instruction.
DATA MEMORY (RAM)
1 word of RAM is composed of 4 bits, but 1-bit manipulation
(with the SB j, RB j, and SZB j instructions) is enabled for the
entire memory area. A RAM address is specified by a data
pointer. The data pointer consists of registers X and Y. Set a
value to the data pointer certainly when executing an instruction
to access RAM.
Table 2 shows the RAM size. Figure 12 shows the RAM map.
Table 2 RAM size
Product
M34250M2
M34250E2
RAM size
64 words
4 bits (256 bits)
0
8
7
6
5
4
3
2
1
Interrupt address page
0000
16
007
F
16
0080
16
00
FF
16
0100
16
017
F
16
0180
16
Subroutine special page
07
FF
16
Page 1
Page 2
Page 0
Page 3
Page 15
0
8
External interrupt address
7
6
5
4
3
2
1
Timer 1 interrupt address
0080
16
0082
16
00FF
16
R
Register X
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0 1
RAM 64 words
4 bits (256 bits)
2 3
64 words
PROGRAM MEMORY (ROM)
The program memory is a mask ROM. 1 word of ROM is
composed of 9 bits. ROM is separated every 128 words by the
unit of page (addresses 0 to 127). Table 1 shows the ROM size
and pages. Figure 10 shows the ROM map of M34250M2.
Table 1 ROM size and pages
Product
M34250M2
M34250E2
ROM size (
9 bits)
2048 words
Pages
16 (0 to 15)