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C
Applications Information: continued
5
To drive the gauges 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.
Figure 2. Definition of serial word.
Table 1. Nominal output for major gauge (V
BB
= 14V).
The 10 bits are shifted into the devices 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
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.
Figure 3. Serial data timing diagram.
Figure 4. Power-up sequence.
10 Bits
V
CC
CS
SI
OE
ST
10 Bits
OUTPUTS
ENABLED
R
S
R
S
OUTPUTS
ENABLED
SO
(tpd)
SO
(Rise, Fall)
10% - 90%
SI
(Hold)
SI
(Setup)
SCLK
SI
SO
CS
Hold
CS
CS
Setup
Input Code
(Decimal)
0
128
256
384
512
640
768
896
1023
Ideal
Degrees
0
45
90
135
180
225
270
315
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
Major
Gauge
(360
°
)
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
D9 D D7 select
which octant
Divides a 45
octant into 128 equal parts
to achieve a .35
resolution
Code 0 D 127
10
MSB
LSB
Application Diagram
ENABLE
CS4172
10k
SCLK
SI
COS-
V
BB
V
CC
COS+
SIN-
SIN+
ST
SO
OE
CS
Microcontroller
Next Driver
360
°
Gauge
V
BAT
V
REG
CS-8156
5V
12V