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 Regis-
ter 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 dis-
play’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 brightness level and set
the sleep mode bit to logic high.
Dot Register
The Dot Register holds the
pattern to be displayed by the
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.
Pixel Map
In a 4-character display, the
160-bits are arranged as 20
columns by 8 rows. This array
can be conceptualized as four 5
x 8 dot matrix character loca-
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.
8
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