Page 104 VRC2000 Installation and Operations Manual
Technical or Setup Assistance
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The microprocessor RST (reset) line is controlled by both the 24-hour clock,
as well as the standby battery-switching network. The VRC2000 was
designed to clamp the microprocessor’s reset line low whenever the 5Vdc
regulator (VR1) drops below 4Vdc, which corresponds to the AC input/line
voltage being a approximately 72Vacrms. This reset/switching network halts
the processor, as well as battery backing up the RAM (user database) and the
real-time clock. This battery backup is provided by the internal 3.6Vdc
lithium battery.
Telephone Logic and Interface
The VRC2000 includes an automatic telephone coupler. Coupling to the
telephone line is accomplished by rectifying ringing voltage to a logic level
and by monitoring loop current. The unit will detect an inbound call when
the AC ringing voltage appears across tip and ring of the LINE telephone
jack. The bridge rectifier, 8R2, smooths the ringing pulses at the U42 input,
an 4N37 opto-isolator which, in turn, triggers the processor ring detect/loop
sense interrupt by driving its output (pin 5) low. The unit will then answer
the line at the programmed number of rings.
Once the VRC2000 is online (telephoneline is terminated) loop current
flows. This also holds the output of the opto-isolator low. For remote
disconnect (hang up) the VRC2000 monitors current reversal or loop-current
drop. If either of these occurs, the unit will return to an on-hook condition.
The VRC2000 uses a NE5900 call-progress decoder to aid in monitoring line
conditions.
The VRC2000 employs a PREM SPT-183 coil as a hybrid coupler. The
microprocessor controls the relays K1 and K2 to provide telephone-line
connection to the coil, or provide voltage to the SET jack in set-up mode.
With Part 68 Registration, limited RFI filtering is provided on the LINE
input. In high RFI fields, additional protection may be required to eliminate
demodulation by the bridge rectifier (BR2) of RFI present on the phone line.
The VRC2000 can be set up to dial up to five telephone numbers when
reporting alarm conditions. The telephone numbers are always dialed in
sequence, one through five, with a 60-second pause between each number.
After the last number, the VRC2000 pauses for 10 minutes before redialing
the first number. If a faster repeat is desired, enter the same telephone
Table 20. Hardware Interrupt Prioritization
Priority U29 Bit Description
1st A8-Pin 9 Real Time Clock (U25, MC146818)
2nd A7-Pin 8 Modem
3rd A6-Pin 7 Interrupt A
4th A5-Pin 6 Interrupt B
5th A4-Pin 5 DTMF Decoder (U18, SSI202)
6th A3-Pin 4 Call Progress Decoder (U13, NE5900)
7th A2-Pin 3 Ring Detect/Loop Sense (U42, 4N37)
Sth Al-Pin 2 Speech Interrupt (U12, MM54104)
Appendix D:
Continued
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