DCAN Control Registers
1088
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
Controller Area Network (DCAN) Module
23.17.6 Test Register (DCAN TEST)
Figure 23-24. Test Register (DCAN TEST) [offset = 14h]
31
16
Reserved
R-0
15
10
9
8
Reserved
RDA
EXL
R-0
R/WP-0
R/WP-0
7
6
5
4
3
2
0
Rx
Tx
LBack
Silent
Reserved
R-U
R/WP-0
R/WP-0
R/WP-0
R-0
LEGEND: R/W = Read/Write; R = Read only; WP = Write Protected by Test bit; -
n
= value after reset; U = Undefined
Table 23-12. Test Register Field Descriptions
Bit
Field
Value
Description
31-10
Reserved
0
These bits are always read as 0. Writes have no effect.
9
RDA
RAM Direct Access Enable
0
Normal Operation
1
Direct access to the RAM is enabled while in Test Mode.
8
EXL
External Loop Back Mode
0
Disabled
1
Enabled
7
Rx
Receive Pin. Monitors the actual value of the CAN_RX pin.
0
The CAN bus is dominant.
1
The CAN bus is recessive.
6-5
Tx
Control of CAN_TX pin
0
Normal operation, CAN_TX is controlled by the CAN Core.
1h
Sample Point can be monitored at CAN_TX pin.
2h
CAN_TX pin drives a dominant value.
3h
CAN_TX pin drives a recessive value.
4
LBack
Loop Back Mode
0
Disabled
1
Enabled
3
Silent
Silent Mode
0
Disabled
1
Enabled
2-0
Reserved
0
These bits are always read as 0. Writes have no effect.
For all test modes, the Test bit in CAN Control Register needs to be set to 1. If Test bit is set, the RDA,
EXL, Tx1, Tx0, LBack, and Silent bits are writable. Bit Rx monitors the state of pin CAN_RX and therefore
is only readable. All Test Register functions are disabled when the Test bit is cleared to 0.
NOTE:
The Test Register is only writable if Test bit in CAN Control Register is set.
Setting Tx to other than 00 will disturb message transfer.
When the internal loop back mode is active (LBack bit is set), EXL bit will be ignored.