Rockwell SoniCrafter BT8960 - Manual (Page 45)

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2.0 Functional Description
2.5 Microcomputer Interface
Bt8960
Single-Chip 2B1Q Transceiver
N8960DSB
A prescaler may precede the timer. This increases the time span available at
the expense of resolution. Only the startup timers have prescalers. Table 2-7 pro-
vides summary information on the timers.
Four timers are provided for use in timing startup events. These timers share a
single prescaler which divides the symbol clock by 1,024 and supplies this slow
clock to the four counters. The timers are: Startup Timer 1, Startup Timer 2,
Startup Timer 3, and Startup Timer 4. Each one is independent, with separate
interval timer values and interrupts.
Two timers control the measurement intervals for the various meters: the SNR
Alarm Timer and the Meter Timer. The SNR Alarm Timer is used only by the low
SNR, while the Meter Timer is used by all other meters, excluding the low SNR
meter. Their respective interrupts for each timer signal are set when they expire.
There are no prescalers for these timers; they count at the symbol rate. Both tim-
ers are normally used in the continuous mode.
Two timers are provided for general use: General Purpose Timer 3 and Gen-
eral Purpose Timer 4. Both timers are identical. There are no prescalers for these
timers; they count at the symbol rate. Each timer signals an interrupt when it
expires.
Table 2-7. Timers
Timer Name Purpose Clock Rate Control Bits
Startup Timer 1 Startup Events Symbol rate ÷ 1024 sut 1
Startup Timer 2 Startup Events Symbol rate ÷ 1024 sut 2
Startup Timer 3 Startup Events Symbol rate ÷ 1024 sut 3
Startup Timer 4 Startup Events Symbol rate ÷ 1024 sut 4
SNR Alarm Timer SNR Measurement Symbol rate snr
Meter Timer Measurement Symbol rate meter
General Purpose Timer 3 Miscellaneous Symbol rate t3
General Purpose Timer 4 Miscellaneous Symbol rate t4