HDSP-2301 HP [Agilent(Hewlett-Packard)], HDSP-2301 Datasheet - Page 12

• Manufacturer Part Number: HDSP-2301
• Description: Four Character 5.0 mm (0.20 inch) 5 x 7 Alphanumeric Displays
• Manufacturer: HP [Agilent(Hewlett-Packard)]

where
Drive Circuit Concepts
A practical display system utiliz-
ing the HDSP-2000 family of
displays requires interfacing with
a character generator, refresh
memory and some timing cir-
cuitry. A block diagram of such a
display system is depicted in
Figure 2. This circuit provides for
ASCII data storage and decoding
and properly refreshes the display
at a 100 Hz refresh rate. In this
figure, the display length is shown
as N characters with the leftmost
display character labeled as char-
acter 1 and the right most
character of the display labeled
as character N. The refreshing of
the display is accomplished by a
series of counters.
Figure 2. CKT Block Diagram
CLOCK
IN
D F
t T T
. .
5
B
t T T
7xNxMx5x100 Hz
T
COUNTER
2
DOWN
m
7
B
sec.
COUNTER
DOWN
(
5
( )
a
5
N
)
The N counter sequentially ac-
cesses N coded information
symbols from the N x 7 RAM.
Note that for the normal configu-
ration of the HDSP-2000 displays,
character 1 is the leftmost charac-
ter, character 4 is the rightmost
character and shift register cas-
cades from left to right. Thus, the
symbol corresponding to charac-
ter N is decoded first, then the
symbol corresponding to charac-
ter (N-1), and the symbol
corresponding to character 1 is
decoded last.
Each coded information symbol is
read from the N x 7 RAM and de-
coded by a 5 x 7 decoder. The
decoder can be selected to de-
code ASCII, EBDIC, or any
customized character font In this
example, the ASCII decoder is or-
ganized as 128 x 7 words of 5 bits
each. The ASCII symbol and row
select information is applied to
the decoder and the decoder out-
puts information for all 5 columns
for the selected row and symbol.
LOG 2 N
COUNTER
DOWN
RAM
Nx7
M
3
ROW SELECT
LOG 2 M
DECODER
COUNTER
HIGH FIRST COUNT IN M
ASCII
5x7
UP
5
COLUMN OUTPUT
5
3
The 7 counter sequentially ac-
cesses all seven rows of each
ASCII symbol. Note that row 7
must be decoded first, then row 6,
and row 1 is decoded last. The
load new serial data into the
HDSP-2000 display. During one
count, the display clock is en-
abled and 7N bits of serial data
are loaded into the display.
During the remaining (M1)
counts, this data is displayed.
Thus the duty factor for the cir-
cuit in Figure 2 is
The 5 counter sequentially re-
freshes all 5 columns of the
display. The outputs of the 5
counter are connected to a data
multiplexer which selects one of
the 5 outputs from the ASCII de-
coder and loads it into the Data
Input of the HDSP-2000 display
string. The 5 counter also en-
ables one of the 5 column driver
4
DECODER
M counter is used to periodically
D F
ENABLE
3
. .
MUX
1/5
M
5
CHARACTER I
M
5
1
.
20 1
5
HDSP-2000
DISPLAY
V CC
V B
M
CHARACTER N
AN1016.02
1
( )
6