4518 Datasheet, PDF (20/160 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4518 Group
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 Z, X, and Y. Set a value to the
data pointer certainly when executing an instruction to access
RAM (also, set a value after system returns from RAM back-up).
Table 2 shows the RAM size. Figure 12 shows the RAM map.
Table 2 RAM size
Part number
M34518M2/M4
M34518M6/M8/E8
• Note
Register Z of data pointer is undefined after system is released
from reset.
Also, registers Z, X and Y are undefined in the RAM back-up. After
system is returned from the RAM back-up, set these registers.
RAM size
256 words ✕ 4 bits (1024 bits)
384 words ✕ 4 bits (1536 bits)
RAM 384 words ✕ 4 bits (1536 bits)
Register Z
0
1
Register X 0 1 2 3 ^... 6 7 ^{... ...} 15 0 ^{... ...} 5 6 7
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
M34518M6 _{Z=0, X=0 to 15}
M34518M8/E8 _{Z=1, X=0 to 7}
M34518M2/M4 Z=0, X=0 to 15
256 words
384 words
Fig. 12 RAM map
Rev.3.01 2005.06.15 page 20 of 157
REJ03B0008-0301