455A Datasheet, PDF (22/148 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

455A 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 power
down mode).
RAM includes the area for LCD.
When writing “1” to a bit corresponding to displayed segment,
the segment is turned on.
Table 9 shows the RAM size. Figure 23 shows the RAM map.
• Note
Register Z of data pointer is undefined after system is released
from reset.
Also, registers Z, X and Y are undefined in power down mode.
After system is returned from the power down mode, set these
registers.
Table 9 RAM size and pages
Part number
M3455AG8
M3455AGC
RAM size
512 words × 4 bits (2048 bits)
RAM 512 words 4 bits (2048 bits)
Register Z
0
1
Register X 0 1 2 3
12 13 14 15 0 1 2 3
12 13 14 15
0
1
2
3
4
5
6
7
8
0 8 16 24
9
1 9 17 25
10
2 10 18 26
11
3 11 19 27
12
4 12 20 28
13
5 13 21 29
14
6 14 22 30
15
7 15 23 31
Note: The numbers in the shaded area indicate the corresponding segment output pin numbers.
Fig 23. RAM map
Rev.1.01 Feb 15, 2008 Page 22 of 146
REJ03B0224-0101