This article is about the British telephone device. See monologue

Monologue

In theatre, a monologue is a speech presented by a single character, most often to express their thoughts aloud, though sometimes also to directly address another character or the audience. Monologues are common across the range of dramatic media...

 for the other definition.

A Monolog is a Single Telephone Line Call Logging Device manufactured by British Telecom in the UK. The reason for connecting Monolog to a telephone line is to collect independent call and charging data to help resolve customer queries or complaints.

Monolog is usually connected to a customer's line at the telephone exchange

Telephone exchange

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

 although it is possible to monitor the line at the customer's premises.

Monolog is based around the Mitsubishi

Mitsubishi

The Mitsubishi Group , Mitsubishi Group of Companies, or Mitsubishi Companies is a Japanese multinational conglomerate company that consists of a range of autonomous businesses which share the Mitsubishi brand, trademark and legacy...

 M50734SP

M50734SP

The M50734 is a high-performance 8-bit single-chip CMOS microcontroller that is fully compatible with Mitsubishi's Series 740 family. This ROM/RAM-less device includes an array of on-chip functions such as UART, Serial I/O, A/D, Watchdog timer, VCU, 32parallel I/O ports. A choice of 8 and 16-bit...

-10 8-bit processor that uses an enhanced 6502

MOS Technology 6502

The MOS Technology 6502 is an 8-bit microprocessor that was designed by Chuck Peddle and Bill Mensch for MOS Technology in 1975. When it was introduced, it was the least expensive full-featured microprocessor on the market by a considerable margin, costing less than one-sixth the price of...

 instruction set. The unit comprises two boards: a digital board that contains EPROM and RAM for storage of call records and an analogue board that provides the necessary interface components to the monitored telephone line.

Monolog is powered via four AA rechargeable batteries which are trickle charged at approximately 2 mA from a control line. This control line is also used for remote connection to the unit for the purposes of data retrieval.

Analogue Board

The analogue board provides the interface circuitry between the monitored and control telephone lines and the microprocessor. The board contains the following devices ;

U1 = OP490 Quad Op-Amp
U2 = Mitel MT8870CE DTMF Decoder
U3 = Motorola MC145442 V.21 300Baud Modem
U4 = LM358N
U5 = Phillips 74HC157P

The board also contain a 25-way female D-type connector that provides the electrical interface to the monitored/control lines. Alternatively, it provides an RS-232 interface thereby enabling the direct connection of a PC running the Dialog software.

Battery Charging circuit

Monolog's batteries can be charged via 2 spare pins on the 25-way D-type connector; pin 4 (RTS) and pin 20 (DTR). If a 12volt power source is applied to either pin, the batteries are charged at 22mA. If both pins are used, the batteries are charged at 44mA. The 12volt feed is via two 330Ω current limiting resistors and the wired in fuse. This circuitry does not provide any protection against over-charging.

Digital Board

The digital board contains 7 Integrated Circuits as follows ;

U1 = M50734-SP10 Mitsubishi Microprocessor
U2 = 74HC373P address latch
U3 = CD4060BCN 14-bit asynchronous binary counter
U4 = 74HC139N Address decoder

Address decoder

In digital electronics, an address decoder is a decoder circuit that has two or more bits of an address bus as inputs and that has one or more device selection lines as outputs. When the address for a particular device appears on the address bus, the address decoder asserts the selection line for...

U5 = Static RAM (130 kB

Kilobyte

The kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...

)
U6 = 27C256BQ EPROM
U7 = Static RAM (32 kB)

In addition to these components are the reverse battery protection diode associated timing circuitry for the Processor and CMOS divider IC.

Real Time Clock

To enable the call records to be date stamped, the CMOS divider IC produces an interrupt pulse every 125 ms which activates the processor. The interrupt service routing updates the system clock and checks for any activity on the line. If there is none, the processor goes back to the SLEEP mode. In this mode, the CPU consumes very little power thereby enabling the unit to be battery powered. In its quiescent state, Monolog consumes around 180 µA while the monitored telephone line is inactive, rising to a peak of about 6 mA during a call while the DTMF decoder is on during the first 20 to 30 seconds of a call.