Applications Information: continued
To drive the gaugeÕs pointer to a particular angle, the
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.
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.
CS
CSHold
CSSetup
MSB
D9
LSB
D0
SCLK
Major
Gauge
(360°)
D8
D7
D6
D5
D4
D3
D2
D1
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 12710
SI
Figure 2. Definition of serial word.
SO(Rise, Fall)
10% - 90%
SO
SO(tpd)
Input Code
(Decimal) Degrees
Ideal
Nominal
Degrees
VSIN
(V)
VCOS
(V)
Figure 3. Serial data timing diagram.
0
0
45
90
135
180
225
270
315
359.65
0.176
45.176
90.176
135.176
180.176
225.176
270.176
315.176
359.826
0.032
10.476
10.476
10.412
-0.032
-10.476
-10.476
-10.476
-0.032
10.476
10.412
-0.032
-10.476
-10.476
-10.412
0.032
128
256
384
512
640
768
896
1023
VCC
CS
SI
10 Bits
10 Bits
10.476
10.476
OE
ST
Table 1. Nominal output for major gauge (VBB = 14V).
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
OUTPUTS
ENABLED
OUTPUTS
ENABLED
Figure 4. Power-up sequence.
Application Diagram
VBAT
5V
VREG
12V
CS-8156
ENABLE
360° Gauge
SIN-
10k
COS+
COS-
VBB
SIN+
ST
VCC
CS
SI
SCLK
CS4172
Microcontroller
SO
Next Driver
OE
5
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
