CS4172
Applications Information: continued
To drive the gaugeÕs pointer to a particular angle, the
microcontroller sends a 10-bit digital word into the serial
port. These 10 bits are divided as shown in Figure 2.
However, from a software programmers viewpoint, a
360¡ circle is divided into 1024 equal parts of .35¡ each.
Table 1 shows the data associated with the 45¡ divisions
of the 360¡ driver.
register changes at SO on the falling edge of SCLK. This
arrangement allows the cascading of devices. SO is
always enabled. Data shifts through without affecting the
outputs until CS is brought low. At this time the internal
DAC is updated and the outputs change accordingly.
CS
CS
Setup
CS
Hold
MSB
Major
Gauge
(360°)
D9
D8
D7
D6
D5
D4
D3
D2
D1
LSB
SCLK
D0
SI
(Setup)
SI
(Hold)
D9 Ð D7 select
which octant
Divides a 45° octant into 128 equal parts
to achieve a .35° resolution
Code 0 Ð 127
10
SI
Figure 2. Definition of serial word.
SO
SO
(Rise, Fall)
10% - 90%
SO
(tpd)
Input Code
Ideal
(Decimal) Degrees
0
0
128
45
256
90
384
135
512
180
640
225
768
270
896
315
1023
359.65
Nominal
Degrees
0.176
45.176
90.176
135.176
180.176
225.176
270.176
315.176
359.826
V
SIN
(V)
0.032
10.476
10.476
10.412
-0.032
-10.476
-10.476
-10.476
-0.032
V
COS
(V)
10.476
10.412
-0.032
-10.476
-10.476
-10.412
0.032
10.476
10.476
Figure 3. Serial data timing diagram.
V
CC
CS
SI
10 Bits
10 Bits
The 10 bits are shifted into the deviceÕs shift register MSB
first using an SPI compatible scheme. This method is
shown in Figure 3. The CS must be high and remain high
for SCLK to be enabled. Data on SI is shifted in on the ris-
ing edge of the synchronous clock signal. Data in the shift
ST
OUTPUTS
ENABLED
REGISTERS
SET TO ZERO
Table 1. Nominal output for major gauge (V
BB
= 14V).
OE
REGISTERS
SET TO ZERO
OUTPUTS
ENABLED
Figure 4. Power-up sequence.
Application Diagram
V
BAT
V
REG
5V
12V
CS-8156
ENABLE
360° Gauge
10k
SIN-
SIN+
ST
CS
SI
SCLK
OE
Microcontroller
CS4172
COS+
COS-
V
BB
V
CC
SO
Next Driver
5
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
