Modem 1200 [Model 1670]
The Commodore 1670, also known as the “Modem/1200”, is Commodore’s first Hayes-compatible modem: It connects directly to the phone line and supports pulse and tone dialing for 1200 and 300 baud duplex connections. There were two revisions, the original 1670 and the “new” 1670, a.k.a. CR-1670. (The unit in this article is the later revision.)
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; Motorola MC14412 |
| 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 |
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.
- four DIP switches (default to down):
| DIP | Description | |
|---|---|---|
| 1 | Auto Answer Enable | down: auto-answer on second ring disabled |
| 2 | Carrier Detect Enable | down: carrier detect on pin H-K of edge connector (needed for Plus/4) |
| 3 | Speed Indicate Enable | down: speed indicate on pin J of edge connector |
| 4 | Data Terminal Ready | down: DTR always on (instead of computer controlled) |
The 1670 is based on a U.S. Robotics (“USR”) chipset:
- U2:
© USR'85 U2J2 / OKI C49-387 / JAPAN 7X2033: This is an OKI MSM80C49-387RS, a 80C49 microcontroller with 2KB of mask ROM and 128 bytes of RAM. “387” indicates which ROM image it contains. - U3:
© USR'85 U3J2 / OKI C49-388 / JAPAN 7Y2013: This is an OKI MSM80C49-388RS, another 80C49 microcontroller, with a different ROM image (“388”). - U4:
© USR86 / USR101 16-249 / S8749 / 35561: This socketed IC is probably the ROM that holds the bulk of the modem’s firmware.
Software (click label to download .d64 disk image):
Side A:
Side B:
[original disk]
[Modem 1200 manual]
[additional material]
- manual missing
