Cypress CY7C65113C manual Suspend Mode, Watchdog Reset

CY7C65113C

7.2Watchdog Reset

The WDR occurs when the internal Watchdog Timer rolls over. Writing any value to the write-only Watchdog Reset Clear Register (Figure 7-1) clears the timer. The timer rolls over and WDR occurs if it is not cleared within tWATCH of the last clear (see Section 23.0 for the value of tWATCH). Bit 6 of the Processor Status and Control Register (Figure 13-1) is set to record this event (the register contents are set to 010X0001 by the WDR). A Watchdog Timer Reset lasts for 2 ms, after which the microcontroller begins execution at ROM address 0x0000.

tWATCH2 ms

Last write to Watchdog Timer Register

No write to WDT register, so WDR goes HIGH

Execution begins at Reset Vector 0x0000

Figure 7-1. Watchdog Reset (Address 0x26)

The USB transmitter is disabled by a Watchdog Reset because the USB Device Address Registers are cleared (see Section 17.1). Otherwise, the USB Controller would respond to all address 0 transactions.

It is possible for the WDR bit of the Processor Status and Control Register (Figure 13-1) to be set following a POR event. If a firmware interrogates the Processor Status and Control Register for a set condition on the WDR bit, the WDR bit should be ignored if the POR bit is set (Bit 3 of the Processor Status and Control Register).

8.0Suspend Mode

The CY7C65113C can be placed into a low-power state by setting the Suspend bit of the Processor Status and Control register. All logic blocks in the device are turned off except the GPIO interrupt logic and the USB receiver. The clock oscillator and PLL, as well as the free-running and Watchdog timers, are shut down. Only the occurrence of an enabled GPIO interrupt or non-idle bus activity at a USB upstream or downstream port wakes the part out of suspend. The Run bit in the Processor Status and Control Register must be set to resume a part out of suspend.

The clock oscillator restarts immediately after exiting suspend mode. The microcontroller returns to a fully functional state 1 ms after the oscillator is stable. The microcontroller executes the instruction following the I/O write that placed the device into suspend mode before servicing any interrupt requests.

The GPIO interrupt allows the controller to wake-up periodically and poll system components while maintaining a very low average power consumption. To achieve the lowest possible current during suspend mode, all I/O should be held at VCC or Gnd. Note: This also applies to internal port pins that may not be bonded in a particular package.

Typical code for entering suspend is shown below:

...	; All GPIO set to low-power state (no floating pins)
...	; Enable GPIO interrupts if desired for wake-up
mov a, 09h	; Set suspend and run bits
iowr FFh	; Write to Status and Control Register – Enter suspend, wait for USB activity (or GPIO Interrupt)
nop	; This executes before any ISR
...	; Remaining code for exiting suspend routine.

Document #: 38-08002 Rev. *D Page 16 of 49

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