The sleep-timer comes up on a regular base and interrupts your running program. This interrupt can be used to wake a PSoC1 from "Sleep-Mode" which is a low-power-state where neither CPU nor most of the peripherals / modules are not running and so not consuming power. The interrupt gives the ability to check the outer world and if nothing happened, go to sleep again.
Additionally the sleep-timer-component can be used to wait, time loops and similar jobs.
The watchdog must be reset by the program from time to time. If this is not done, it will reset the PSoC and start all over again. Watchdog is ment to capture a situation where the CPU goes into an infinite-loop and to restart without human interaction.
thanks for the reply. but i am yet to understand the sleep mode completely. can you suggest any document which describes the "sleep" mode in detail. like how a device enters a sleep mode, what actually is the CPU doing in the sleep mode. and how a device comes out of the sleep mode etc.
Check out AN2223. This shows how a naked op amp can be created using an SC block. Though this does not give you all the three terminals of the op amp on pins, maybe you could use this op amp for your application.