PDSP1880, PDSP1881, PDSP1882, PDSP1883, PDSP1884
Functional Description
Theory of Operation
The display's user interface is organized into five memory areas.
They are accessed using the Flash Input, FL, and address lines,
A3 and A4. All the listed RAMs and Registers may be read or writ-
ten through the data bus. See Table „Memory Selection“ (page 9).
Each input pin is described in Pin Definitions.
The PDSP188X Display is designed to work with all major micro-
processors. Data entry is via an eight bit parallel bus. Three bits of
address route the data to the proper digit location in the RAM.
Standard control signals like WR and CE allow the data to be writ-
ten into the display.
D0–D7 data bits are used for both Character RAM and control
word data input. A3 acts as the mode selector. If A3=1, character
RAM is selected. Then input data bit D7 will determine whether
input data bits D0–D6 is ASCII coded data (D7=0) or UDC data
(D7=1). See section on „UDC Address Register and UDC RAM“
(page 10).
Five Basic Memory Areas
Character RAM
Stores either ASCII (Katakana)
character data or an UDC RAM
address
Flash RAM
1 x 8 RAM which stores Flash data
For normal operation FL pin should be held high. When FL is held
low, Flash RAM is accessed to set character blinking.
User-Defined
Character RAM
(UDC RAM)
Stores dot pattern for custom
characters
The seven bit ASCII code is decoded by the Character ROM to
generate Column data. Twenty columns worth of data is sent out
each display cycle, and it takes fourteen display cycles to write into
eight digits.
User-Defined Address
Register (UDC Address
Register)
Provides address to UDC RAM
when user is writing or reading
custom character
The rows are multiplexed in two sets of seven rows each. The
internal timing and control logic synchronizes the turning on of
rows and presentation of column data to assure proper display
operation.
Control Word
Register
Enables adjustment of display
brightness, flash individual
characters, blink, self test or clearing
the display
Power Up Sequence
Upon power up the display will come on at random. Thus the dis-
play should be reset on power-up. Reset will clear the Flash
RAM, Control Word Register and reset the internal counter. All
the digits will show blanks and display brightness level will be
100%.
RST can be used to initialize display operation upon power up or
during normal operation. When activated, RST will clear the Flash
RAM and Control Word Register (00H) and reset the internal
counter. All eight display memory locations will be set to 20H to
show blanks in all digits.
The display must not be accessed until three clock pulses (110 µs
minimum using the internal clock) after the rising edge of the reset
line.
FL pin enables access to the Flash RAM. The Flash RAM will set
(D0=1) or reset (D0=0) flashing of the character addressed by A0–
A2.
Microprocessor Interface
The 1 x 8 bit Control Word Register is loaded with attribute data if
A3=0.
The interface to a microprocessor is through the 8-bit data bus
(D0–D7), the 4-bit address bus (A0–A3) and control lines FL, CE
and WR.
The Control Word Logic decodes attribute data for proper imple-
mentation.
To write data (ASCII/Control Word) into the display CE should be
held low, address and data signals stable and WR should be
brought low. The data is written on the low to high transition of
WR.
Character ROM is designed for 128 ASCII characters. The ROM
is Mask Programmable for custom fonts.
The Clock Source could either be the internal oscillator
(CLKSEL=1) of the device or an external clock (CLKSEL=0) could
be an input from another HDSP211X display for synchronizing
blinking for multiple displays.
The Control Word is decoded by the Control Word Decode Logic.
Each code has a different function. The code for display brightness
changes the duty cycle for the column drivers. The peak LED cur-
rent stays the same but the average LED current diminishes
depending on the intensity level.
The Display Multiplexer controls the Row Drivers so no additional
logic is required for a display system.
The character Flash Enable causes 2.0 Hz coming out of the
counter to be ANDED with the column drive signal to make the col-
umn driver cycle at 2.0 Hz. Thus the character flashes at 2.0 Hz.
The Display has eight digits. Each digit has 35 LEDs.
Memory Selection
FL
0
A4
X
0
A3
X
0
Section of Memory
Flash RAM
A2–A0
Data Bits Used
D0
Character Address
Don’t Care
1
UDC Address Register
UDC RAM
D3–D0
1
0
1
Row Address
Character Address
Don’t Care
D4–D0
1
1
1
Character RAM
D7–D0
1
1
0
Control Word Register
D7–D0
2006-03-30
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OSRAM [ OSRAM GMBH ]
