ZHCSJK5C January 2018 – October 2020 TCAN4550-Q1
The TCAN4550-Q1 contains a watchdog (WD) timeout function. When using the WD timeout function the WD runs continuously. The WD is default enabled and can be configured with four different timer values. WD is active in normal and standby modes and off in sleep mode. Once the device enters standby or normal mode the timer does not start until the first input trigger event. This event can be either writing a one to register 16'h0800 or if selected, by changing the voltage level on the GPIO1 pin either high or low when configured for watchdog input. If the first trigger is not set the watchdog is disabled. The first trigger can happen in standby mode or normal mode. This is system implementation specific. While the timer is running, a SPI command writing a one to 16'h0800 resets the WD_TIMER timer or if configured for pin control the GPIO1 behaves as the watchdog input bit.
The TCAN4550-Q1 has two ways of setting the trigger bit: via a SPI command and, if selected, through a GPI (GPIO1 configured as GPI). When a GPI pin is used any rising or falling edge resets the timer. A watchdog event can be conveyed back to the microprocessor in two methods: interrupt on nINT pin or, if selected, the GPO2 pin can be programmed to toggle upon a WD timeout. A timeout can initiate one of three actions by the TCAN4550-Q1: interrupt, INH toggle plus putting the device into standby mode or toggle watchdog output reset pin if enabled. The input CLKIN or crystal values needs to be entered into reg 16'h0800 and is either 20 MHz or 40MHz. See Table 8-2 for the register settings for the watchdog function.
00 = 60 ms
01 = 600 ms
10 = 3 s
11 = 6 s
CLKIN/Crystal frequency reference
0 = 20 MHz
1 = 40 MHz
00 = No action
01 = M_CAN_INT 0 interrupt (active low)
10 = Watchdog output
11 = Mirrors nINT pin
a 1 to reset timer: if times out; this bit is set and then the
selected action from register 16'h0800[17:16] takes place.
Note: This is a self-clearing bit. Writing a 1 resets the timer and then the bit clears.
Selected action when WD_TIMER times out
00 = Set interrupt flag and if a pin is configure to reflect WD output as an interrupt the pin shows a low.
01 = Pulse INH pin and place device into standby mode – high - low - high ≈300ms
10 = Pulse watchdog output pin if enabled – high - low - high ≈300ms
11 = Reserved
Note: Interrupt flag is always set for a WD timeout event.
Pin Function Select
00 = GPO
01 = Reserved
10 = GPI – Automatically becomes a WD input trigger pin.
11 = Reserved
|3||WD_EN||RXU||1'b1||WD_EN - Watchdog
0 = Disable
1 = Enabled