S
P
IA
S
O
M
I
Internal Connection Logic
M3 GPIO Mux
S
S
I3
F
ss
SSI3Clk
S
S
I3
R
x
C28 GPIO Mux
S
P
IA
C
LK
S
P
IA
S
IM
O
S
PI
AS
T
E
M3
S
S
I3
P
e
ri
p
h
e
ra
l
C28
S
P
I‐
A
P
e
rip
h
e
ra
l
SSI3Fss_in
SSI3Fss_out
SSI3Clk_in
SSI3Clk_out
SSI3Rx_in
SSI3Tx_out
SPIASTE_in
SPIASTE_out
SPIACLK_in
SPIACLK_out
SPIASOMI_in
SPIASOMI_out
SPIASIMO_in
SPIASIMO_out
SERPLOOP[SSI3TOSPIAE]
SERPLOOP[SSI3TOSPIAM]
C28 SPI-A to M3 SSI3 Internal Loopback
999
SPRUHE8E – October 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
C28 Serial Peripheral Interface (SPI)
Figure 12-12. SSI and SPI Connections for Loopback Mode
shows the three loopback modes available. Loopback mode is disabled by default. The
SERPLOOP register in the M3 system control register space determines the loopback mode.
Configuration of SERPLOOP is only available on the M3 master subsystem. Three different modes are
available: not connected (default), M3 SSI3 master connected to C28 SPI-A slave, and M3 SSI3 slave
connected to C28 SPI-A master. For a detailed description of the SERPLOOP register, refer to the
System
control and Interrupts
chapter.
Table 12-7. Loopback Modes
SERPLOOP[SSI3TOSPIAE]
SERPLOOP[SSI3TOSPIAM]
Mode
0
x
Not Connected (default on
reset)
1
0
M3 SSI3 Master connected to
C28 SPI-A Slave
1
1
M3 SSI3 Slave connected to
C28 SPI-A Master
Legend: 0 = Bit cleared, 1 = Bit set, X = Any
12.2.1 Loopback Initialization and Configuration
To enable M3 SSI3 master to C28 SPI-A slave loopback mode, perform the following steps:
1. Enable and configure the M3 SSI module as a SPI master by following the steps outlined in the
Initialization and Configuration section of the
M3 Synchronous Serial Interface (SSI)
chapter.
2. Enable the corresponding loopback mode by setting SERPLOOP[SSI3TOSPIA] = 0x2 on the M3
subsystem.
3. Enable and configure the C28 SPI module as detailed in
.
To enable M3 SSI3 slave to C28 SPI-A master loopback mode, perform the following steps: