PD243X Datasheet, PDF (3/7 Pages) OSRAM GmbH – Alphanumeric Programmable Display

Figure 3. PD2435 block diagram showing the major blocks
and internal registers
A push button is interfaced to port P3.2 of the SAB 80535 to
provide an external interrupt to the microcontroller.
8
D0 – D7
DISPLAY
MEMORY
(RAM)
4x8
4
CTL
REG
1x8
7 DECODE
&
CE0, CE1
MIX
A0 – A2
RD, WR
5
14
8
128 CHAR.
ROM
48 x 80
OUTPUT
CONTROL
LOGIC
1
15
OUTPUT
LATCH
1
20
3
CLK SEL
XCK
RST
OSC
LOGIC
DISPLAY
3
MULTI-
PLEXER
20
7
DISPLAY
COLUMN
DRIVERS
3
ROW
DRIVERS
Application
The speed regulated moving message display is an example
where a digitized value of the controlling analog signal is used
to compute a reload value for the Timer 2. The Timer 2 is oper-
ated in mode 0 where this reload value becomes a starting
point for the Timer to count up. On overflow the Timer automat-
ically takes the restart value for counting from reload register
CRC. While the Timer is counting up, a new reload value is
computed using the present A/D value.
Hardware
The circuit used in this application has the advantage of requir-
ing a minimum of components. The single chip microcomputer
SAB 80535 operates in conjunction with four alphanumeric
programmable display chips PD 2435 to form a 16-digit long
display.
The ASCll-coded data is transferred from the SAB 80535 to the
display ICs via the data port P0 and using the control signal WR
(P3.6) of the SAB 80535. The address pins from the ports P0
and P2 of the SAB 80535 are used to address the EPROM as
well as the display chips in a memory-mapped l/O scheme. The
display chips are addressed as memory locations with the fol-
lowing addresses.
Display
Chip
1
2
3
4
Control Register
Address
1000H
2000H
4000H
8000H
Digits Address
1004H-1007H
2004H-2007H
4004H-4007H
8004H-8007H
Firmware Description
Besides controlling speed of the moving message, there is a
provision to interrupt the moving message and roll it backwards
to the beginning of the message. The microcontroller reads the
code and the message to display from an EPROM 2716A inter-
faced to the ports P0 and P2 of the SAB 80535. A virtual image
of the message is created in the internal RAM of the SAB
80535. Four display chips PD2435 are interfaced to the SAB
80535 in a memory-mapped scheme and can be addressed as
external memory to the SAB 80535. The virtual image of the
message in internal RAM of the SAB 80535 is used to manipu-
late data to be displayed on the display chips. The internal RAM
used for the display can be viewed as an area divided into two
portions:
1. For active display
2. As a data buffer
The active display area is the replica of the data being displayed
on the display chips. In this case the 16-digit display would need
16 RAM locations which correspond to 16 digits currently being
displayed. The data buffer contains the rest of the message
which is not being displayed. The message is shifted character
by character in the RAM area. When the message on the dis-
play moves from right to left, the RAM buffer acts in “First In
First Out” mode, and when the message on the display moves
from left to right, the data to the display from the microcontrol-
ler RAM buffer is supplied in the “Last In First Out” scheme.
Between display of every character there is a software delay
which depends upon the level of the analog signal supplied to
the ANO pin of the SAB 80535. The external interrupt 0 (at port
P3.2) is used to interrupt the microcontroller to inform it that
the message needs to be scrolled backwards. On getting this
interrupt the software sets the flag bit 0 which remains set until
the message is scrolled back to the beginning of the message.
List of Components
Name
SAB 80535
271 6A
PD2435
12 MHz Crystal
74LS373
22 pF Capacitors
100 nF Capacitor
4.7 µf Capacitor
1 k Resistor
10 k Pot
Number
1
1
4
1
1
2
1
1
1
1
Reference Material for ICs
1. SAB 80515/80535 User’s Manual.
2. PD2435 Data-Sheet or Optoelectronic Data Book (1990).
 2000 Infineon Technologies Corp. • Optoelectronics Division • San Jose, CA
www.infineon.com/opto • 1-888-Infineon (1-888-463-4636)
OSRAM Opto Semiconductors GmbH & Co. OHG • Regensburg, Germany
www.osram-os.com • [phone]
3
Appnote 49
May 31, 2000-14