Hardware description
13
SLLU216 – July 2019
Copyright © 2019, Texas Instruments Incorporated
SPI to CAN FD SBC + LIN Transceiver BoosterPack User's Guide
When in test mode the GPIO1 pin is used to provide the input signal for the transceiver (TXD_INT_PHY)
or the input to the M_CAN core (RXD_INT_CAN). This is accomplished by first putting the device into test
mode using register 16'h0800[21] = 1 and then selecting which part of the device is to be tested by setting
register 16'0800[0].
Pin 5 of the LaunchPad connection header is connected to the GPIO1 pin. Furthermore, since GPIO1 can
be used as an interrupt status pin, an LED has also been added to this pin as a visual indicator to the user
on the status of this pin and buffered through a transistor to prevent excessive loading on the device pin.
However, since the GPIO1 is a negative logic indicator when used for interrupts, the signal is first inverted
through an additional transistor such that the LED is illuminated when the GPIO1 pin is low indicating a
device interrupt has occurred.
2.4.6
TCAN4550-Q1 Wake Request (nWKRQ)
The nKWRQ pin is a dedicated wake up request pin from a bus wake (WUP) request, local wake (LWU)
request and power on (PWRON). The nWKRQ pin is defaulted to a wake enable based upon a wake
event. In this configuration the output is pulled low and latched to serve as an enable for a regulator that
does not use the INH pin to control voltage level. The nWKRQ pin can be configured by setting
16'h0800[8] = 1 as an interrupt pin that pulls the output low but once the wake interrupt flag is cleared
releases the output back to a high. This pin defaults to an internal 3.6 V rail that is active during sleep
mode. In this configuration, if a wake event takes place, the nWKRQ pin switches from high to low. This
output can be configured to be powered from the V
IO
rail through SPI programming, 16'h0800[19]. When
powered off the V
IO
pin the device does not insert an interrupt until the V
IO
rail is stable. When configured
for V
IO
this pin is an open drain output and requires an external pull-up resistor V
IO
rail. This configuration
bit is saved for all modes of operation and is not reset in sleep mode. As some external regulators or
power management chips may need a digital logic pin for a wake up request this can be used.
NOTE:
This pin is active low and is the logical OR of CANINT, LWU and WKERR register 16'h0820
that are not masked.
If a pull-up resistor is placed on this pin it must be configured for power from the V
IO
rail
2.4.7
TCAN4550-Q1 Reset (RST)
The TCAN4550-Q1 RST pin is a device reset pin. It has a weak internal pull down resistor for normal
operation. If communication has stopped with the TCAN4550-Q1 the RST pin can be pulsed high and then
back low for greater than t
PULSE_WIDTH
to perform a power on reset to the device. This resets the device to
the default settings and puts the device into standby mode. If the device was in normal or standby mode
the INH and nWKRQ pins remain active (on) and do not toggle. If the device is in sleep mode and reset is
toggled the device enters standby mode and at that time INH and nWKRQ turns on.
After a reset has taken place a wait time of
≥
700 µS should be used before reading or writing to the
TCAN4550-Q1.
2.4.8
TLIN2029-Q1 Transmit (TXD)
TXD is the interface to the MCU's LIN protocol controller or SCI and UART that is used to control the state
of the LIN output. When TXD is low the LIN output is dominant (near ground). When TXD is high the LIN
output is recessive (near V
BATTERY
). The TXD input structure is compatible with microcontrollers with 3.3-V
and 5-V I/O. TXD has an internal pull-down resistor. The LIN bus is protected from being stuck dominant
through a system failure driving TXD low through the dominant state time-out timer.
2.4.9
TLIN2029-Q1 Receive (RXD)
RXD is the interface to the MCU's LIN protocol controller or SCI and UART, which reports the state of the
LIN bus voltage. LIN recessive (near V
BATTERY
) is represented by a high level on the RXD and LIN
dominant (near ground) is represented by a low level on the RXD pin. The RXD output structure is an
open-drain output stage. This allows the device to be used with 3.3 V and 5 V I/O microcontrollers. If the
microcontoller's RXD pin does not have an integrated pullup, an external pullup resistor to the
microcontroller I/O supply voltage is required. In standby mode the RXD pin is driven low to indicate a
wake up request from the LIN bus.
