IC-TW11 Datasheet, PDF (12/25 Pages) IC-Haus GmbH – 10-BIT ULTRA LOW POWER MAGNETIC ABSOLUTE ROTARY ENCODER

iC-TW11 10-BIT ULTRA LOW POWER^preliminary
MAGNETIC ABSOLUTE ROTARY ENCODER
SPI COMMUNICATION
Rev B1, Page 12/25
The iC-TW11 SPI port is a 4-wire slave interface which
operates in CPOL = 0 and CPHA = 0 mode only (SPI
Mode 0). This means that the base (resting) value of
SCLK (pin 10) is low, SI (pin 5) is sampled on the rising
edge of SCLK, and SO (pin 7) is changed on the falling
edge of SCLK. The active-low slave select input, xSS
(pin 11), is used by the host µP to enable the SPI port
to initiate communication. Data is transferred with MSB
first.
SPI communication uses an overlapped packet struc-
ture where the response to a command is returned while
the next command is being sent. Figure 5 shows this
for a single-device application (where the host controls
a single iC-TW11 slave). See BUSSING MULTIPLE ICs
on page 22 and CHAINING MULTIPLE ICs on page 23
for multiple device applications.
xSS
SI
16 bits
1
Command
16 bits
2
Command
16 bits
3
Command
16 bits
4
Command
16 bits
5
Command
0
1
2
3
4
SO
Response
Response
Response
Response
Figure 5: SPI overlapped packet structure
SPI command and response packets are always 16
bits long. The host initiates communication with the
iC-TW11 by driving slave select (xSS) low and then
clocking a 16-bit command (1) to the slave input, SI.
The serial clock (SCLK) signal is not shown in Figure 5.
The host drives xSS high at the end of the command
packet and the iC-TW11 executes the command.
After waiting for the command to be executed (or for
the iC-TW11 to assert IRQ_OUT), the host again drives
xSS low and sends the next command packet (2) to SI
while at the same time reading the 16-bit response (1)
to the initial command (1) on the slave output, SO.
The iC-TW11 always returns a response packet while
reading a command packet. The response packet (0)
returned while writing the first command packet (1) is
not defined. Likewise, the response packet returned
after a register write command is not defined.
SPI COMMAND AND RESPONSE PACKET FORMAT
Command packet format
Command packets sent to the iC-TW11 by the host are
formatted as shown in Table 6.
A write command is one in which wr (bit 14) is 1. The
data (bits 7-0) is written to the register at the specified
address (bits 13-8).
Command Packet
Bit
Name
15
sup
14
wr
13:8
address
7:0
data
Description
Suppress new sample
Write Data to Address
6-bit Register Address
8-bit Register Data
Table 6: Command packet format
A read command is one in which the write bit, wr, (bit
14) is 0. The register at the specified address (bits 13-8)
is read and its contents returned in the next response
packet. Data (bits 7-0) are ignored.
The suppress bit, sup (bit 15), when set (1) suppresses
the next sample. This is useful when using external
sampling or when reading sine and cosine data to en-
sure simultaneously-sampled values. Normally, sup =
0.
Response packet format
The format of response packets depends on the spe-
cific register that is read (see Table 8 on the following
page). The response packet returned following a write
command is undefined.