Display Overview
The HCMS-39XX series is a
family of LED displays driven by
on-board CMOS ICs. The LEDs
are configured as 5x7 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.
Eight-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.
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
Figure 5.
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.
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
↑
CE
↓
L
RS
L
X
L
Not Rising
↑
L
H
↓
L
H
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.
10
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
