20T202DA5EB Pacer Components, 20T202DA5EB Datasheet - Page 8

• Manufacturer Part Number: 20T202DA5EB
• Description: Vacuum Fluorescent Display
• Manufacturer: Pacer Components

2X20 VFD Module with 2-Wired Interface
5. FUNCTION DESCRIPTIONS
5.1 Registers in VFD Controller
* Truth Table for Register Selection
The VFD controller has two 8-bit registers, an instruction register (IR) and a data register (DR). IR stores instruction
codes, such as display clear and cursor shift, and address information for DD-RAM and CG-RAM. The IR can only
be written from the host MPU. DR temporarily stores data to be written into DD-RAM. Data written into the DR from
the MPU is automatically written into DD-RAM or CG-RAM by an internal operation. By the register selector (RS)
signal, these two registers can be selected.
5.1.1 Address Counter (ACC)
5.1.2 Display Data RAM (DD-RAM)
Display data RAM (DD-RAM) stores display data represented in 8-bit character codes. The area in DD-RAM that is
not used for display can be used as general data RAM. See below Table for the relationships between DD-RAM
addresses and positions on the VFD.
5.1.3 Character Generator ROM (CG-ROM)
5.1.4 Character Generator RAM (CG-RAM)
including cursor. Valid CG-RAM addresses are 00H to 3FH. CG-RAM not being used to define characters can be
used as general purpose RAM (lower 5 bits only). Character codes from 00H to 07H (or 08H to 0FH) are assigned to
the user-definable characters (refer to Appendix-1 for Character Font Tables). The table on next page shows the
relationship between the character codes, CG-RAM addresses, and CG-RAM data for each user-definable character.
The address counter (ACC) assigns addresses for both DD-RAM and CG-RAM. When an instruction of address is
written into the IR, the address information is sent from the IR to the ACC. Selection of either DD-RAM or
CG-RAM is also determined concurrently by the instruction. After writing into DD-RAM or CG-RAM, the ACC
automatically increased by 1.
* The Relationships Between DD-RAM Addresses and Positions on the VFD
The character generator ROM (CG-ROM) generates character patterns of 5*7 dots from 8-bit character codes. It can
generate 240 kinds of 5*7 dot character patterns. The character fonts are shown on the Fig.-10. The character codes
00H to 0FH are allocated to the CG-RAM.
The CG-RAM stores the pixel information (1=pixel on, 0=pixel off) for the eight user-definable 5*7 characters
2nd ROW
RS
1st ROW
0
1
IR writes as an internal operation (display clear, etc.)
DR writes as an internal operation (DR to DD-RAM or CG-RAM)
1st Column
00 Hex
40 Hex
2nd Column
01 Hex
41Hex
Operation
20T202DA5EB (Rev.1.0)
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3rd Column
02 Hex
42 Hex
………
………
………
19th Column
12 Hex
52 Hex
Fig.-9 Dot Assignment
11
16
21
26
31
1
6
12
17
22
27
32
20th Column
2
7
13 Hex
53 Hex
13
18
23
28
33
36
3
8
14
19
24
29
34
4
9
10
15
20
25
30
35
5