Instruction manual
Hardware Overview
025-9416 17
An uninterruptible power supply (UPS) option (Part No. 802-9049) obtains standby power from
storage batteries and keeps the system operating through brownouts and blackouts. Zetron’s stan-
dard UPS is a 400 VA unit with built-in batteries that provide 30 minutes of emergency power.
Higher capacity UPS options may be available as required. Other UPS equipment can provide
more capacity and can even power radio equipment. For applications assistance, contact the
Zetron Mobile and Paging Systems Division.
The power supply is protected by a 1 amp UL approved fuse (item #11, Figure 3). The fuse can
be checked or replaced by unscrewing the cover counter-clockwise.
MAIN PROCESSOR MOTHERBOARD
Advanced large-scale integrated (LSI) circuits comprise an entire computer onto the 8-in × 14-in
main processor motherboard (Part No. 702-9673). The main processor (item #2, Figure 2)
includes 2 MB or more of volatile DRAM (item #3, Figure 2). Paging software loaded from the
plug-in ROM disk (item #6, Figure 2) at power-on operates in the DRAM memory, and acts as
traffic manager and diagnostic maintenance controller of the microprocessors on the peripheral
motherboard (item #4, Figure 2).
Paging Terminal Timing
The main processor board contains power-on reset timing and a watchdog circuit to help recover
from any software faults or high-energy noise interference. The watchdog timer must be written
to by the system once a second to keep it from initializing a reset pulse.
A real-time clock also provides the central timing for the PCM digitized audio highway used by
the peripheral motherboard for passing audio to and from the trunks and station output.
PCM Highway
The PCM highway is composed of three signals: data, clock, and sync. Data is a time-multi-
plexed serial signal and can be encoded and decoded by the trunk or station sections of the
Model 640. The clock signal is a 1.544 MHz square wave, which synchronizes the serial data.
Eight clock pulses constitute a slot. Audio is converted into 8-bit words and presented in one slot.
24 slots constitute a frame. The sync pulse marks the beginning of a frame and is one clock cycle
of duration with a period of about 125 microseconds (8 kHz sampling rate). Each slot can be
thought of as a channel carrying unidirectional audio information (just like a radio channel).
Voice Prompts And Storage
The main processor board is the source of all the telephone prompts. Prompting tones are gene-
rated on dedicated PCM channel slots for 1 kHz beep, out of service whoop, telco dial tone, telco
ringing sound, and telco busy sound.
Voice recording and playback functions are also performed on the main processor board (DAPT
XTRA only). Voice to and from the PCM highway is compressed or expanded using ADPCM
transcoders. The compressed live voice data is stored in the EMS area of DRAM. Compressed
voice prompts are stored on the battery backed non-volatile RAM disk.