9
RS
T
RSS
1
T
RSH
2
CE
T
CLKCE
3
T
CES
4
T
CLKH
11
T
CLKL
12
T
CEH
5
CLK
[1]
T
DS
6
T
DH
7
NEW DATA LATCHED HERE
D
IN
T
CEDO
10
T
DOUT
8
D
OUT
(SERIAL)
T
DOUTP
9
D
OUT
(SIMULTANEOUS)
LED OUTPUTS,
CONTROL
REGISTERS
PREVIOUS DATA
NEW DATA
NOTE:
1. DATA IS COPIED TO THE CONTROL REGISTER OR THE DOT LATCH AND LED OUTPUTS WHEN CE IS HIGH AND CLK IS LOW.
HCMS-29xx Write Cycle Diagram
Control Register
The Control Register allows
software modification of the IC’s
operation and consists of two
independent 7-bit control words.
Bit D
7
in the shift register selects
one of the two 7-bit control
words. Control Word 0 performs
pulse width modulation
brightness control, peak pixel
current brightness control, and
sleep mode. Control Word 1 sets
serial/simultaneous data out
mode, and external oscillator
prescaler. Each function is
independent of the others.
columns by 8 rows. This array can
be conceptualized as four 5 x 8
dot matrix character locations,
but only 7 of the 8 rows have
LEDs (see Figures 1 & 2). The
bottom row (row 0) is not used.
Thus, latch location 0 is never
displayed. Column 0 controls the
left-most column. Data from Dot
Latch locations 0-7 determine
whether or not pixels in Column 0
are turned-on or turned-off.
Therefore, the lower left pixel is
turned-on when a logic high is
stored in Dot Latch location 1.
Characters are loaded in serially,
with the left-most character being
loaded first and the right-most
character being loaded last. By
loading one character at a time
and latching the data before
loading the next character, the
figures will appear to scroll from
right to left.
logic high and then CE is brought
to logic low. Next, each
successive rising CLK edge will
shift in the data on the D
IN
pin.
Finally, when 8 bits have been
loaded, the CE line is brought to
logic high. When CLK goes to
logic low, new data is copied into
the selected control word.
Loading data into the Control
Register takes place while the
previous control word configures
the display.
Control Word 0
Loading the Control Register with
D
7
= Logic low selects Control
Word 0 (see Table 2). Bits D
0
-D
3
adjust the display brightness by
pulse width modulating the LED
on-time, while Bits D
4
-D
5
adjust
the display brightness by
changing the peak pixel current.
Bit D
6
selects normal operation or
sleep mode.
Control Register Data
Loading
Data is loaded into the Control
Register, MSB first, according to
the procedure shown in Table 1
and the Write Cycle Timing
Diagram. First, RS is brought to
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