The Target Modem #
The target device here is a Best Data 56k PC Card Data / Fax Modem. It boasts adherence to the V.90 standard, which had a whopping maximum download speed of 53.3Kbps, and an upload speed of 33.6Kbps.
The form factor is a Type II PCMCIA card, with a 14-pin connector on the other end that mates with a custom cable to an analog phone jack.
Inside the Case #
At first glance, there are a few interesting observations with this PCB. Firstly, the PCB is very thin, only 0.4 mm thick and feels very flexible. Secondly, there is a bodge wire travelling between the two sides of the board through a cutout that holds a transformer.
The Major Silicon #
- AMD AM29F002T - 2Mbit CMOS (5.0 Volt-only) Flash Memory. Flash Dump: Project 56k Flash AM29F002T TSOP32.BIN
- ISSI IS61C1024L-15T - 1024 Kbit CMOS 8-bit SRAM
- (U1) Atmel 24C02N - Two Wire Serial EEPROM 2048 Kbit
- Rockwell RCDL56DPFL - Modem Data Pump
- Rockwell P39W/U - Presumably the microcontroller
Inside the Firmware #
Using binwalk on the file extracted from the AMD flash does not give any interesting information. Using strings however does give some information that is helpful, including the following items:
| String found | Presumed reference |
|---|---|
| ROCKWELL;ADPCM;8 | Potential reference to Adaptive differential pulse-code modulation |
| ROCKWELL AC/K56 V2.083- | Reference to the firmware version |
| Smart One 56SPC V.90 Fax Data Modem | Product name |
| 56000/24000/19200/14400 | Presumed baud rates |
What is the P39W/U Microcontroller? #
Unfortunately for this project, there are sparse references on the internet for a Rockwell P39W/U. Based on findable datasheets like this one for a different Rockwell modem device set, it is likely an 8-bit microcontroller and L1902-11 is the ordering code.
Additional hints are available through cpu-world.com, where a user CPUShack was selling some of the L39 back in 2019. They describe these parts as:
The Rockwell L39 (and P39/C39 like it) are a 14MHz 65C02 processor.
This is an enhanced 6502 core made on a CMOS process and can run at 3.3V
This includes 12 new bit manp instructions and 21 new arithmetic instructions
These are New Old Stock
15x Rockwell L3903-59 L39/A/U 65C02 Processor $5 each or a pair for $7
Without additional research or disassembly attempts, this is as far as I can take it.
