CSL-8308 Exhibit E
To File  Date October 18, 1983
From L. Stewart  Location PARC
Subject CSL-8308 Registration Organization CSL
Release as /Indigo/Voice/Documentation/RegistrationExhibitE.tioga
Came from
 /Indigo/Voice/Documentation/RegistrationExhibitE.tioga
Last editedby L. Stewart, October 18, 1983 2:52 pm
Abstract This document contains Exhibit E to be included with FCC Form 730 for the Part 68 registration application for the CSL-8308 Voice Terminal.
1.0 General
This exhibit contains a description of all electrical circuitry and mechanical construction affecting compliance with the requirements of Subpart D of Part 68 of the FCC rules.
The CSL-8308 Voice Terminal uses solid state audio, switching, and control circuits. The power supply and interface to the telephone network contain dielectric barriers to protect the internal circuits from external stresses such as hazardous voltages and lightning. Protecting the internal circuits of the CSL-8308 assures compliance with most of the requirements of Part 68. The remaining requirements, such as signal power limits, are met by design.
This exhibit begins with a discussion of basic system structure. Then the telephone network port interface is discussed in detail, describing how the various components affect compliance with the rules. The power supply and mechanical construction are covered next, leading into a discussion of each test and how the CSL-8308 design fulfills the requirements of that test.
2.0 Hardware Description
2.1 General
Diagram E-1 is a block diagram of the CSL-8308 Voice Terminal. The 8308 is a microprocessor based multifunction terminal intended for applications in office system research. External connections are made to the 8308 for power, telephone network, separately registered telephone set (a standard 2500 type single line instrument), non-registered analog voice devices, and digital interfaces for communications with other office equipment. Each external connection will be considered below for its affects on compliance with the requirements of Part 68.
The 8308 is designed around an analog switch. The switch handles all voice interconnections between the various sources and sinks except for signals bound to the telephone network interface. Signals bound for the telephone network are handled specially in order to meet the signal power limitations of Part 68. The analog switch is controlled by a pair of microprocessors which have the additional functions of handling digital voice and of digital communications with other office equipment.
2.2 External connections
The external power connection is to standard 120 v AC mains. The power supply isolation transformer construction and insulation provides isolation between the AC mains and both the telephone network and non-registered equipment and circuits.
The telephone network connection includes both telephone connections (tip and ring) and auxiliary connections (A and A1). The telephone network port circuits fully isolate these connections from all other circuits through a dielectric barrier.
The telephone instrument is separately registered. The 8308 incorporates a power-fail line transfer relay which connects the telephone instrument directly to the telephone network.
Connections to non-registered analog voice equipment falls into two groups: those for input only and those for output only. The voice input ports are the microphone (for speakerphone service), and two line-level audio inputs (for music-on-hold). The outputs are a loudspeaker and two line-level audio outputs.
There are two digital communications ports, TTY and Ethernet. The TTY port is intended for communications with low bit-rate devices such as computer terminals, the Ethernet port is a high bit-rate connection to the Experimental Ethernet local area network.
2.3 Telephone network interface
Diagram E-2 is a block diagram of the telephone network interface. Diagrams E-3-A and E-3-B are detailed schematic diagrams of those portions of the CSL-8306 affecting compliance with Part 68. The Central Office (CO) line is isolated from all other circuits by four dielectric barriers, two relays, a transformer, and an opto-isolator. Thus the CO line is floating and has no connection to ground except that provided by a secondary protection device.
2.3.1 Protection circuits
On entry to the 8308, tip and ring of the CO line pass through protection circuits consisting of a TII-47BT gas-tube surge suppressor and through 100 microhenry and 10 ohm resistors for RFI isolation. The surge suppressor qualifies as a secondary protection device.
2.3.2 Ring detector
The CO line, now refered to as tipA and ringA in the drawings, connects to the light emitting side of a TI TIL119 opto-isolator. Capacitor C40 is rated at 600 volts and serves to connect the opto-isolator only for AC ringing current. The ringer equivalence number of the internal ring detect circuit is established by the resistance of R58 and by the impedance of capacitor C40. The dielectric barrier of the opto-isolator is rated at 1500 volts and serves to protect the internal control circuits of the 8308. Components R58 and C40 also determine the on hook impedance of the 8308. They are selected to comply with the requirements of Section 68.312 (On-Hook Impedance Limitations).
2.3.3 Line Relay
Diodes D9, D10, D11, and D12 are rated at 1000 volts each. The bridge formed by these diodes serves to establish proper operating polarity for the electronic holding coil discussed below. Relay K1 is the 8308's line relay; when closed, it establishes a conducting path for CO loop current. The dielectric barrier between coil and contacts is rated at 1000 vrms and serves to protect the internal control circuits of the 8308.
2.3.4 Power-fail transfer
Lines tipA and ringA also connect to the power-fail transfer circuit. Relay K3 serves as the power-fail transfer relay. In the event of a power failure, the separately registered telephone set connected to the 8308 is cut through directly to the CO telephone line via K3. This set will typically have a bridged ringer. Relay K3 is of the same type as relay K1 and is rated for 1000 vrms breakdown.
The telephone set does not involve hazardous voltage sources and floats on tip and ring assuring longitudinal balance requirements are met. In any event, the power-fail transfer mode is not a normal operating condition and would be corrected quickly as in this mode the customer would experience loss of all terminal-provided services except power-fail transfer.
2.3.5 Electronic holding coil
After passing through the line relay K1, the CO line is referred to as SwLine+ and SwLine- ("Switched Line"). These signals connect to the electronic holding coil circuit surrounding transistor Q2. This circuit is a current source with operating current set by the value of R98 to approximately 38 mA. Zener diode D23 diverts surge currents below the threshold of the gas tube supressor discussed above.
2.3.6 Isolation transformer
Capacitor C43 isolates the line side of transformer T1 from the off hook voltage across the electronic holding coil. It serves no role in electrical protection. Transformer T1 provides the main dielectric barrier between the CO line and the internal circuits of the 8308. Its dielectric is rated at 1250 vrms. The longitudinal balance of the CO line is not affected by the termination on the secondary side because the transformer provides isolation.
2.3.7 Telephone interface circuits
The circuits on the secondary side of transformer T1 form a single transformer hybrid. Zener diodes D13 and D14 provide a final level of protection for the internal circuits from any surge voltages which pass through the transformer. The signal path from the telephone line travels to the analog switch for further distribution. The signal path to the telephone line comes only from the digital to analog conversion section of the Intel 2910/2912 codec/filter.
2.3.8 Signal power limitations
Out-of-band signal power is limited by the low pass anti-aliasing filter section of the Intel 2912A. In-band signal power limits are enforced by the microprocessor portion of the 8308. Both these matters will be described in additional detail. Signal power limits are not adjustable.
2.4 Connections to non-registered equipment
No special circuitry is included in the interface circuitry to non-registered equipment either to provide dielectric isolation from the internal circuits of the 8306 or to provide signal power limitations. Rather, these functions are provided by the telephone network port as described above.
The CSL-8308 has two ports for connection of non-registered voice or audio devices, Line In A and Line In B. These ports are intended for music-on-hold application. In addition, there is a port intended for the connection of a microphone for speakerphone service (live voice).
Other non-registered external equipment includes a loudspeaker, line-level outputs, and digital communications interfaces. These devices do not affect compliance with Part 68.
2.5 Connections to separately registered equipment
A standard 2500 type desk telephone set is normally connected to the CSL-8308. In the power-fail transfer mode, this set is cut through directly to the CO line. In normal operation, however, the telephone set is connected to the analog switch. In this mode, the voice and signaling path from the telephone set to the CO line passes through the same filtering and level limiting functions as all other signal sources except network address signaling. The telephone included with the CSL-8308 is registered under FCC Registration Number AS293P-70088-TE-T and has a ringer equivalence number of 1.0A.
2.6 Digital communications
The microprocessor in the 8308 includes interfaces for digital communications with other office equipment by EIA RS-232 and by the Xerox Experimental Ethernet local area network. The RS-232 interface is intended for communications with low bit-rate devices such as computer terminals. The Ethernet interface is intended for communications with office workstation computers.
2.7 Power Supply
The CSL-8308 Voice Terminal incorporates a Condor TD-60W linear regulated power supply. For further electrical isolation, an isolation transformer is included which incorporates transformer dielectric in excess of 1500 vrms. All secondary outputs of the power supply are non-hazardous and operate at plus 5 volts for digital logic, and plus and minus 12 volts for operational amplifiers. The 8308 does not incorporate a ringing generator to drive the telephone set ringer. All primary circuits are well separated from the secondary circuit wiring.
Diagram E-4 shows circuits on the primary side of the power supply. Diagrams E-5-A and E-5-B are the manufacturer's parts list and schematics.
2.8 Mechanical construction
The CSL-8308 package consists of a metal case enclosing circuit boards and power-supply. The external dimensions are 12.5 inches high, 5 inches wide, and 13.5 inches deep. The case consists of top and bottom solid covers, perforated sides, front "connector" panel, and rear "power supply" panel. The entire case and secondary circuit ground is electrically connected to the power cord "green" earth ground terminal and considered to be an exposed conducting surface.
The top and bottom covers include permanently mounted pem nuts. The sides, front, and rear panels attach to the top and bottom covers with 28 screws.
The power supply panel supports the power supply, circuit breaker, and IEC power cord connector. Secondary leads from the power supply are cabled together and connect to the "digital" board via a latching connector.
The connector panel supports the "digital" and "analog" circuit boards. The digital board is attached to the panel by the mounting screws for the Ethernet and TTY connectors. The analog board is attached to the panel by two angle brackets. The angle brackets attach to studs permanently welded to the panel. The digital and analog boards form a sandwich. The front edge of each board is attached to the connector panel as described above. The boards are interconnected at their rear edges by a latching interboard connector. During shipping, card guides are installed on the top and bottom covers for addtional board support.
2.9 Photographs
The following photographs are attached:
Photo 1: Top view of analog board, showing locations of telephone network interface components
Photo 2: Bottom view of analog board, showing locations of telephone network interface circuits
Photo 3: View of board sandwich from analog side, showing connector panel mounting
Photo 4: View of connector panel, showing various connector locations
Photo 5: View of power supply assembly, showing wiring practices.
Photo 6: View of completed unit showing connector panel, top, and one side panel
3.0 Testing
3.1 General
This section discusses each test performed on the CSL-8308 Voice Terminal as called for in Part 68 of the rules.
3.2 Section 68.314 -- Billing protection
The telephone network interface circuits assure compliance with this section of the rules.
68.314 (b) (1) -- On-Hook Signal Power. Relay K1 breaks both tip and ring when on-hook. Low leakage across the open contacts of this relay assure that the requirements are met.
68.314 (c) -- Loop Current. When K1 is closed (off-hook), the electronic holding coil draws more current from the loop than would be drawn by a 200 ohm resistor.
68.314 (d) -- Signaling Interference. All tone sources in the system meet this requirement. The music-on-hold port does not include a notch filter, but has very fast rolloff above 3400 Hz.
3.3 Section 68.312 -- On-Hook Impedance Limitations
68.312 (b) (1) The telephone network interface circuits and ringer used in the power-fail transfer mode affect compliance with the rules of this section. In the power-fail transfer mode, the bridged ringer of the telephone set controls the on-hook impedance. The telephone set is separately registered under FCC Registration Number AS293P-70088-TE-T. In normal operation, on-hook impedance is controlled by the series combination of R58 and C40.
68.312 (b) (2) The CSL-8308 is intended for use on facilities which always will have additional ringing detection circuitry in place.
3.4 Section 68.310 -- Longitudinal Balance Limitations
In normal operation longitudinal balance is controlled by the CO line circuit. Since the circuit is floating with no ground connection on the network side of the barrier, compliance is assured. In the power-fail mode, longitudinal balance is controlled by the balance of the separately registered telephone set.
3.5 Section 68.308 -- Signal Power Limitations
This section includes limits on the maximum in-band and out-of-band signal power delivered to the network from any equipment connected to the network.
The CSL-8308 limits signal power by digital means. All signals reaching the CO line interface circuits are first digitally encoded. Network signaling signals are generated by the 8308 in digital form. Music-on-hold and live voice signals bound for the telephone network are converted to digital form and digitally processed before being converted back to analog and passed to the CO line interface circuits.
Signals for network signaling are internally generated by the 8308 so that the power delivered to the loop simulator circuit will be less than 0 dBm averaged over 3 seconds.
Signals from the music-on-hold and live voice ports are converted to digital form inside the 8308. They then pass through a digital power limiting circuit before before being converted back to analog form. Out-of-band signals are attenuated by the Intel 2912A low-pass filter in two ways, on A/D conversion and again on D/A conversion. The characteristics of this filter meet the ATT D3/D4 channel bank specifications. The combined filter characteristic results in 28 dB attenuation at 4000 Hz and 64 dB attenuation above 4600 Hz.
68.308 (b) (1) (i) Non-signaling in-band power. The digital limiting circuit limits the average power of non-live-voice signals to less than -10.5 dBm. Limiting is set to this limit so that no manufacturing variations among the analog components in the CO line interface circuits could cause the level to exceed -9 dBm at the telephone network port. The digital limiting circuit operates by inserting 2.5 dB of loss whenever the level at the telephone network approaches -10.5 dBm. The loss is increased in 2.5 dB steps up to 20 dB. Since the digital circuitry clips at a level of + 5.7 dBm, the 20 dB range of attenuation is sufficent to limit any signal which can be represented in digital form. These settings are not adjustable.
68.308 (b) (2) (i) Signaling power. Signals for network signaling are internally generated by the 8308 so that the power delivered to the loop simulator circuit will be less than 0 dBm averaged over 3 seconds. Since the signals are generated in digital form, there are no tolerances. The level is not adjustable.
68.308 (b) (3) Through-transmission requirements. In normal operation, the CSL-8308 does not include a through-transmission capability. In power-fail transfer mode, the CSL-8308 does not provide loop current.
68.308 (b) (4) (iv) Data Terminal Equipment. The CSL-8308 is not Data Terminal Equipment, but nevertheless complies with the restrictions of this section by providing a non-adjustable level of no greater than -9 dBm.
68.308 (b) (5) Through-transmission gain requirements. The CSL-8308 provides for through transmission only in power-fail transfer mode. In this mode, the CSL-8308 provides neither gain nor loss.
68.308 (c) (1) Power in the 3995-4005 Hz band. The CSL-8308 does not incorporate internal signal sources other than for network signaling.
68.308 (c) (2) Power in the 3995-4005 Hz band, through transmission. The CSL-8308 provides for through transmission only in power-fail transfer mode. In this mode, the CSL-8308 provides neither gain nor loss.
68.308 (d) Longitudinal voltage. The network interface port circuitry is transformer coupled and not connected to ground. By design, the 8308 cannot produce any longitudinal voltages.
3.6 Section 68.306 -- Hazardous Voltage Limitations
The CO line circuit assures compliance with this section. This is apparent because the circuit on the network side of the dielectric barrier is floating with respect to ground and because the delectric barrier complies with the leakage current requirements of section 68.304. Internal amplifiers in the 8308 are powered by plus and minus 12 volts, and so cannot produce larger voltages under any possible failure conditions. The zener diodes D13, D14, and D23 provide additional protection.
3.7 Section 68.304 -- Leakage Current Limitations
Leakage currents are controlled by the dielectrics in the CO line circuit and by the dielectric in the power isolation transformer.
The CSL-8308 contains external leads which fall into several categories:
(1) Telephone connections: tip and ring, found on terminals 3 and 4 of the Telewall connector.
(2) Power connections: line and neutral, found on the outboard terminals of the IEC power connector.
(3) (4) and (5) All these categories are grouped together. The exposed metal case of the 8308 is connected to earth ground and to the ground terminal of the power supply secondary. All connections to non-registered equipment have low-impedance to earth ground. Terminals for connection to non-registered equipment include all terminals on the 8308 except the power cord, the Telewall connector (which is for connection to the telphone network), and the Telephone connector (which connects to the separately registered telephone and which is used in power-fail transfer mode).
(6) Auxiliary leads. A and A1 leads are found on terminals 2 and 5 of the Telewall connector.
Note (a). Both the telephone connections (1) and the auxiliary leads (6) are equipped with a secondary protective device rated at 350 volts. These devices intentionally connect the telephone connections and auxiliary leads to earth ground when voltages to ground exceed 350 volts.
4.0 List of Figures
E-1 Block diagram showing internal structure and external connections.
E-2 Block diagram of the telephone network interface.
E-3-A, E-3-B, Schematic diagrams of the telephone network interface.
E-4 Schematic diagram of power supply primary circuits.
E-5-A, E-5-B Power supply specifications and parts list.
E-6 Intel 2912A data sheet.
5.0 Parts lists
5.1 Power supply primary components
Circuit breaker: Airpax R11-4-1.00A-BO2EV, rated at 1 Ampere.
Isolation transformer: Triad N-68E, rated at 1500 Vrms, refert to attached E-6..
Power supply: Condor TD-60W. See figures E-5-A and E-5-B.
5.2 Telephone network interface components
Secondary protective device: TII-47BT, rated at 350 volts
L1, L2 RFI inductors: 100 microhenrys
R92, R93 RFI resistors: 10 ohms, 1/4 watt
C40 ring detect capacitor: 0.1 microfarad, 600 volts
R58, ring detect resistor: 22K ohms, 1/4 watt
D26, ring detect catch diode: 1N4148, 60 volts
U21, ring detect opto-isolator: Texas Instruments TIL119, rated 1500 volts
D9 - D12, bridge rectifier: 1N4007 diodes, rated 1000 volts and 1 ampere
K1, K3, relays: Midtex 190-22E100, rated 1000 vrms, refer to attached E-7
D23, holding coil protective diode, 1N5363, 5 watt zener, rated 35 volts
R96, holding coil resistor: 4.7 K ohms, 1/4 watt
R97, holding coil resistor: 68 ohms, 1/4 watt
R98, holding coil resistor: 18 ohms, 1/4 watt
Q2, holding coil transistor: 2N3904, rated 60 volts
C43, off-hook DC blocking capacitor: 22 microfarads, rated 35 volts
T1, hybrid and isolation transformer: Midcom 671-0339, rated 1250 vrms, refer to attached E-8
D13, D14, protective diodes: 1N4273A rated 3.0 volts, 500 milliwatts
U2, low-pass filter: Intel 2912A, refer to attached E-9
6.0 Additional information
6.1 Redialing
The CSL-8308 does not incorporate an automatic re-dialing facility.