AD822 datasheet(54/88 Pages) AD

54 / 88 page

ADuC841/ADuC842/ADuC843

Rev. 0 | Page 54 of 88

TIME INTERVAL COUNTER (TIC)

A TIC is provided on-chip for counting longer intervals than

the standard 8051 compatible timers are capable of. The TIC is

capable of timeout intervals ranging from 1/128 second to 255

hours. Furthermore, this counter is clocked by the external

32.768 kHz crystal rather than by the core clock, and it has the

ability to remain active in power-down mode and time long

power-down intervals. This has obvious applications for remote

battery-powered sensors where regular widely spaced readings

are required.

Six SFRs are associated with the time interval counter, TIMECON

being its control register. Depending on the configuration of the

IT0 and IT1 bits in TIMECON, the selected time counter regis-

ter overflow clocks the interval counter. When this counter is

equal to the time interval value loaded in the INTVAL SFR, the

TII bit (TIMECON.2) is set and generates an interrupt if enabled.

If the part is in power-down mode, again with TIC interrupt

enabled, the TII bit wakes up the device and resumes code

execution by vectoring directly to the TIC interrupt service

vector address at 0053H. The TIC-related SFRs are described in

Table 24. Note also that the time based SFRs can be written

initially with the current time; the TIC can then be controlled

and accessed by user software. In effect, this facilitates the

implementation of a real-time clock. A block diagram of the

TIC is shown in Figure 56.

The TIC is clocked directly from a 32 kHz external crystal on

the ADuC842/ADuC843 and by the internal 32 kHz ±10% R/C

oscillator on the ADuC841. Due to this, instructions that access

the TIC registers will also be clocked at this speed. The user

should ensure that there is sufficient time between instructions

to these registers to allow them to execute correctly.

8-BIT

PRESCALER

HUNDREDTHS COUNTER

HTHSEC

SECOND COUNTER

SEC

MINUTE COUNTER

MIN

HOUR COUNTER

HOUR

TIEN

INTERVAL TIMEOUT

TIME INTERVAL COUNTER INTERRUPT

8-BIT

INTERVAL COUNTER

TIMER INTVAL

INTVAL

INTERVAL

TIMEBASE

SELECTION

MUX

TCEN

32.768kHz EXTERNAL CRYSTAL

ITS0, 1

COMPARE

COUNT = INTVAL

Figure 56. TIC, Simplified Block Diagram

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