The Commodore Modem/300 (Model 1660)

The Commodore 1660, also known as the “Modem/300”, is Commodore’s first full-featured modem: It connects directly to the phone line and supports pulse and tone dialing for 300 baud duplex connections.

Historical Context

Year Name Model Description
1982 VICMODEM 1600 connected to phone’s handset connector; manual dialing through phone; Motorola MC14412
1982 AUTOMODEM 1650 connected to phone line, pulse dialing in software
1985 MODEM/300 1660 added tone dialing support by feeding SID output into modem; Texas Instruments TMS99532A
1987 MODEM/1200 1670 Hayes command set; pulse and tone dialing in hardware; 300/1200 baud support; U.S. Robotics chipset

Photos

On the front, there is the user port connector. On the left, there is a switch that can be put into the “A” (answer) or “O” (originate) position, depending whether a phone call is supposed to be made or accepted.

On the back, there are

  • two phone line connectors. “LINE” is connected to the telephone network, and an existing telephone can be connected to the “PHONE” line.
  • an RCA audio connector. The circuitry in the modem only does the 300 baud data transmission part once the telephone connection is established – tone dialing is done by using software to generate the audio using the C64’s sound chip, which is looped into this connector! (Pulse dialing is also done in software, by timing on-hook and off-hook events.)

The label on the bottom says:

C= commodore
MODEL NO. 1660
SERIAL NO. 158297
COMPLIES WITH PART 68, FCC RULES; FC

REGISTRATION NUMBER BR 9608-15671-DM-E

RINGER EQUIVALENT 0.4A 0.6B; JACK (USOC) RJ11
CERTIFIED TO COMPLY WITH CLASS B LIMITS,

PART 15, SUBPART J OF FCC RULES. SEE

INSTRUCTIONS IF INTERFERENCE TO RADIO

RECEPTION IS SUSPECTED.
FCC ID BR 9608-1660

MADE IN: HONG KONG 310476-01

The board is marked “MAGIC MODEM TI-1660” and “ARTWORK NO. 310484 REV 4”. The “TI” might stand for “Texas Instruments”, the manufacturer of the TMS99532A modem chip on the top left of the board, which is the central component of the device.

There is a speaker glued to the top shell that allows monitoring the audio data on the line.

The modem comes with one phone cable.


And there are two cables that connect the C64’s audio output to the modem:

  • The DIN to RCA cable takes the audio signal from the C64/C128 AV connector. It is used if the C64 is connected to a TV through the RF connector, so the AV connector is available.
  • The RCA Y-cable takes the audio signal from the monitor cable. This is used if the C64 is connected to a monitor using the AV connector.

Page 8 in the manual visualizes this:

Box


Manuals

More Box Contents

Disk

Further Reading

Build the ECM-103, an Originate/Answer Modem, Byte Magazine Volume 08 Number 03

2 thoughts on “The Commodore Modem/300 (Model 1660)”

  1. About pulse dialing: it’s actually done by taking the line on and off hook rapidly. It doesn’t use audio signaling like tone dialing does, so I don’t think the audio interconnect on the 1660 was used for pulse dialing.

    I used a 1660 to connect to QuantumLink back in the day. That was pretty painful at 300bps and the 1670 was a welcome upgrade.

    • Thanks; you are right. I clarified the text about pulse and tone dialing in the article.

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