IC-TW14 Datasheet, PDF (25/33 Pages) IC-Haus GmbH – IC-PMX Companion Chip

iC-TW14
iC-PMX Companion Chip
SSI MULTITURN INTERFACE
Rev A1, Page 25/33
The SSI multiturn interface is an SSI slave port used
to transmit the multiturn absolute position calculated by
the iC-TW14 to a singleturn absolute sensor such as
iC-LG, iC-MHM, iC-MU, iC-MN, etc. The number of mul-
titurn and synchronization bits are programmable and
must be set to match the connected singleturn absolute
sensor.
MRDY
MCL
…
MDI
SSI Multiturn Data
0
Figure 4: SSI Multiturn Interface
Pin MRDY high and STATUS.NOSSI = 0 indicate that
the iC-TW14 is ready to transmit its absolute position.
Once MRDY goes high after power-up, the singleturn
absolute sensor (master) sends clock pulses to pin MCL
and the iC-TW14 clocks out the multiturn data on pin
MDI. A single trailing 0 is provided by the iC-TW14 as
shown in Figure 4. All data is binary (not Gray) coded
and sent MSB first.
The iC-TW14 changes the data on pin MDI after each
rising edge of MCL. After the complete data packet is
sent, MDI stays low until the clock pulses on MCL stop.
After the clock pulses stop, MDI is set high after the
SSI timeout delay. MRDY stays high until power-down
unless a fault occurs.
Complete
Multiturn
Position
SSI Data
SSI_MT [31:16]
SSI_MT [15:0]
SSI_ST•
32/360
SSI_LENGTH
SSI_MSB
Figure 5: SSI Multiturn Data
The total length of the SSI data packet is specified
by SSI_LENGTH and the starting bit by SSI_MSB.
Up to 31 total bits of the complete multiturn position
(SSI_MT.SSI_ST) can be sent.
For example, to send SSI data packets containing 16
multiturn bits and one synchronization bit to the exter-
nal singleturn absolute sensor, set SSI_MSB = 15 and
SSI_LENGTH = 17. This case is shown in Figure 5.
The complete multiturn position is formed by concate-
nating the two SSI_MT register values with SSI_ST as
shown in Figure 5. SSI_ST is first converted from de-
grees
to
a
5-bit
binary
number
by
multiplying
by
32
360
so
that the bits represent fractions of a revolution. Thus
the MSB of the converted SSI_ST value represents one
half of a revolution, the next bit represents one quarter,
etc. These bits can be used as synchronization bits by
the external singleturn absolute sensor.
If the iC-TW14 is not ready to transmit data over
the SSI multiturn interface (pin MRDY low and STA-
TUS.NOSSI = 1) and the master singleturn absolute
sensor sends clock pulses to pin MCL, pin MDI stays
high for 32 clock cycles. In this case there is no trailing
0, but a trailing 1. This trailing 1 can be used by the
singleturn absolute sensor to detect invalid multiturn
position data from the iC-TW14.