bt8970 Mindspeed Technologies, bt8970 Datasheet - Page 36

• Manufacturer Part Number: bt8970
• Description: Single-chip Hdsl Transceiver
• Manufacturer: Mindspeed Technologies

2.0 Functional Description
2.5 Microcomputer Interface
timer decrements. There are three 8-bit registers: the Timer Restart Register [timer_restart; 0x0C], the Timer
Enable Register [timer_enable; 0x0D], and the Timer Continuous Mode Register [timer_continuous; 0x0E].
These registers control the operation of the timers. Each bit of the 8-bit registers corresponds to a timer. Each
logic-high bit in timer_restart acts as an event that causes the corresponding timer to reload. Each logic-high bit
in timer_enable acts to enable the corresponding timer. Each logic- high bit in timer_continuous acts to reload
the counter after timing out.
Upon reaching zero, an interrupt is generated if enabled by the Interrupt Mask Low Register [mask_low_reg,
mask_high_reg; 0x02, 0x03]. The interrupt is edge-triggered so that only one interrupt will be caused by a
single time out.
the startup timers have prescalers.
Table 2-7. Timers
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.
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 are set when each of these two timers expire. There
are no prescalers for these timers; they count at the symbol rate. Both timers are normally used in the continuous
mode.
timers are identical. There are no prescalers for these timers; they count at the symbol rate. Each timer signals
an interrupt when it expires.
2-18
For each of the eight timers, there is a 2-byte timer interval register that determines the value from which the
Each counter is loaded with the value in its interval register. The counter decrements until it reaches zero.
A prescaler may precede the timer. This increases the time span available at the expense of resolution. Only
Four timers are provided for use in timing startup events. These timers share a single prescaler which divides
Two timers control the measurement intervals for the various meters: the SNR Alarm Timer and the Meter
Two timers are provided for general use: General Purpose Timer 3 and General Purpose Timer 4. Both
General Purpose Timer 3
General Purpose Timer 4
SNR Alarm Timer
Startup Timer 1
Startup Timer 2
Startup Timer 3
Startup Timer 4
Timer Name
Meter Timer
Preliminary Information/Conexant Proprietary and Confidential
Table 2-7
SNR Measurement
Startup Events
Startup Events
Startup Events
Startup Events
Miscellaneous
Miscellaneous
Measurement
provides summary information on the timers.
Purpose
Conexant
Symbol rate 1024
Symbol rate 1024
Symbol rate 1024
Symbol rate 1024
Symbol rate
Symbol rate
Symbol rate
Symbol rate
Clock Rate
Single-Chip HDSL Transceiver
Control Bits
meter
sut 1
sut 2
sut 3
sut 4
snr
t3
t4
100101B
Bt8970