8
Display Overview
The HCMS-29xx series is a family
of LED displays driven by
on-board CMOS ICs. The LEDs
are configured as 5 x 7 font
characters and are driven in
groups of 4 characters per IC.
Each IC consists of a 160-bit shift
register (the Dot Register), two
7-bit Control Words, and refresh
circuitry. The Dot Register
contents are mapped on a
one-to-one basis to the display.
Thus, an individual Dot Register
bit uniquely controls a single
LED.
8-character displays have two ICs
that are cascaded. The Data Out
line of the first IC is internally
connected to the Data In line of
the second IC forming a 320-bit
Dot Register. The display’s other
control and power lines are
connected directly to both ICs. In
16-character displays, each row
functions as an independent
8-character display with its own
320-bit Dot Register.
Reset
Reset initializes the Control
Registers (sets all Control
Register bits to logic low) and
places the display in the sleep
mode. The Reset pin should be
connected to the system power-on
reset circuit. The Dot Registers
are not cleared upon power-on or
by Reset. After power-on, the Dot
Register contents are random;
however, Reset will put the
display in sleep mode, thereby
blanking the LEDs. The Control
Register and the Control Words
are cleared to all zeros by Reset.
To operate the display after being
Reset, load the Dot Register with
logic lows. Then load Control
Word 0 with the desired bright-
ness level and set the sleep mode
bit to logic high.
LEDs. Data is loaded into the Dot
Register according to the
procedure shown in Table 1 and
the Write Cycle Timing Diagram.
First RS is brought low, then CE
is brought low. Next, each
successive rising CLK edge will
shift in the data at the D
IN
pin.
Loading a logic high will turn the
corresponding LED on; a logic
low turns the LED off. When all
160 bits have been loaded (or 320
bits in an 8-digit display), CE is
brought to logic high.
When CLK is next brought to
logic low, new data is latched into
the display dot drivers. Loading
data into the Dot Register takes
place while the previous data is
displayed and eliminates the need
to blank the display while loading
data.
Dot Register
The Dot Register holds the
pattern to be displayed by the
Pixel Map
In a 4-character display, the
160-bits are arranged as 20
Table 1. Register Truth Table
Function
Select Dot Register
Load Dot Register
D
IN
= HIGH LED = "ON"
D
IN
= LOW LED = "OFF"
Copy Data from Dot Register to Dot Latch
Select Control Register
Load Control Register
[1][3]
Latch Data to Control Word
[2]
CLK
Not Rising
↑
L
Not Rising
↑
L
CE
↓
L
H
↓
L
↑
RS
L
X
X
H
X
X
Notes:
1. BIT D
0
of Control Word 1 must have been previously set to Low for serial mode or High for simultaneous mode.
2. Selection of Control Word 1 or Control Word 0 is set by D
7
of the Control Shift Register. The unselected control word retains its
previous value.
3. Control Word data is loaded Most Significant Bit (D
7
) first.
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