Much to my annoyance, this dongle doesn't implement any sort of standard USB serial profile; it requires a driver to initialize it and presumably to speak some special protocol to it. Keyspan didn't include a Linux driver, the bastards, and since my Powerbook runs Linux with only brief adventures into MacOS, the dongle has been sitting in a box getting dusty.
A little while ago, however, I became curious about the contents of the dongle. Not for any particular reason; I simply succumbed to the hacker's desire to take things apart and see how they work. Well, when I popped the plastic case, what to my startled eyes should appear but an Anchor Chips AN2131SC and a TI 75LV4737A! A few minutes with an ohmmeter and I'd traced out all the interesting connections (see below).
Basically, the Keyspan USB adaptor is a general-purpose reprogrammable USB-enabled 8051-compatible microcontroller, plus a level shifter for RS232 use. The other ICs on the board are a transient suppressor for the USB port, and a 16-byte EEPROM to store Keyspan's USB vendor/product/serial numbers. The 8051 has 8K of RAM and runs at 24 MHz.
Of course, if I'd actually been paying attention to the linux-usb mailing list (instead of procmailing it all into a file I never read), I'd have known this earlier, and also that Brian Warner has already written custom firmware for the dongle to talk to the Linux kernel. But what I'm interested in is not using this as a serial adaptor, but as using it as a relatively cheap ($40) USB experimentation platform.
The design of the adaptor is very straightforward. The USB lines come in, go past a SN75240 transient suppressor, and connect to the EZ-USB chip. The RS232 lines go through the RS232 driver/receiver and connect to UART and general-purpose IO pins on the EZ-USB chip. The boot EEPROM is attached to SCL and SDA, as you would expect. For extra hackability, the spare I/O pins (most of port B) are brought out to extra solder pads on the board. Attaching extra circuitry to these should be trivial, but remember they use 3.3v logic levels.
| EZUSB signal | AN2131 pin | 75LV4737 pins | DB-9 pin | RS232 signal |
|---|---|---|---|---|
| PC0/RxD0 | 14 | Rcvr 1 | 2 | RXD |
| PC1/TxD0 | 15 | Driver 1 | 3 | TXD |
| PC2 | 16 | Driver 2 | 7 | RTS |
| PC3 | 17 | Rcvr 2 | 8 | CTS |
| PC4 | 18 | Rcvr 3 | 6 | DSR |
| PC5 | 19 | Rcvr 5 | 9 | RI |
| PC6 | 20 | Rcvr 4 | 1 | CD |
| PC7 | 21 | Driver 3 | 4 | DTR |
| PB1 | 25 | !EN or STBY | - | |
| Vss | - | 5 | GND | |
IMHO, the fact that this dongle can probably be made into a simple and effective USB prototyping platform is really cool, and I want to get this information out here where it might do someone some good.
To try this you'll need an EZ-USB downloader such as ezdownload (part of the ezload utility). This works on BSD and Linux; you might have to hack on it a little since the userland USB interface is still changing. If you want to make changes, you'll also need the sdcc compiler.
All the demo does is cause some of the pins on the DB9 connector to toggle at 1.9 Hz. You can hook up an LED and a 2.2 kΩ resistor (conveniently, RS232 swings both ways, so you don't need to worry about which way you connect the LED). It should be perfectly safe to run this demo on your dongle, but don't sue me if it breaks something or voids your warranty.
| Model | Description |
|---|---|
| USA-19 | This is the "PDA adaptor" I pulled apart and described, above. It has one DB9 port and is in a translucent case. It's probably the most hackable model (because it has a few unused pins) and also the cheapest. |
| USA-28 |
This is the two-port adaptor in the opaque case. It's basically similar to what I've described, except:
|
| USA-19Q | Appears to be a 1-port version of the USA-28, except that it uses an ADM213E for the level shifter. |
| USA-28X |
This is the two-port adaptor in the translucent case. It's
substantially different from the USA-28! It contains an AN2136SC
instead of a '2131, and instead of using the on-chip UART it has two
OX16C950s,
one per port. It also has
only a single oscillator (12MHz again), the
two expected 75'776s, etc.
The 16'950 seems like a nice chip for serial comms — 15 Mbps, IrDA, 128-byte fifo, blah, blah — but this means you can't easily use this model as a general parallel I/O device just by bypassing the on-chip UART. |
| USA-19W | Keyspan is also advertising a one-port serial adaptor in a black case which has different capabilities from the USA-19. Like the -28X, this also contains a separate Oxford UART chip. This gives it a higher speed (230kbps instead of 57.6kbps) but again makes it less useful for generic I/O. (Thanks to Stephen Malinowski for this info.) |
| USA-19QW | Keyspan's web site mentions this as a follow-on to the -19W. According to Stuart Northfield this contains an AN2136SC, a 16C950, and an ADM213E — it's a combination of the -19Q and the -19W, reasonably enough. |
| USA-19HS |
Brian Onn reports that the -19HS contains, not an Anchor/Cypress chip, but a
TI TUSB3410.
This is like the AN21xx family in that it's an 8052 core with a USB interface, but it's not
compatible with the others. The USA-19HS contains:
|
The -19Q and -19QW both contain an LED connected to a spare pin on the microcontroller. It should be easy to modify the blinkeyspan demo to blink this light instead (just change the port and bitmask in timer0_isr()).
Here are the connections to the '2131 and the level shifter in the USA-19Q. (Thanks to Ray Gannon for all of the information on the -19Q.)
| EZUSB signal | AN2131 pin | ADM213E pins | DB-9 pin / RS232 signal or other function |
|
|---|---|---|---|---|
| PC0/RxD0 | 14 | Rcvr 5 | 2 | RXD |
| PC1/TxD0 | 15 | Driver 1 | 3 | TXD |
| PC2 | 16 | Driver 2 | 7 | RTS |
| PC3 | 17 | Rcvr 1 | 8 | CTS |
| PC4 | 18 | Rcvr 3 | 6 | DSR |
| PC5 | 19 | Rcvr 4 | 9 | RI |
| PC6 | 20 | Rcvr 2 | 1 | CD |
| PC7 | 21 | Driver 3 | 4 | DTR |
| Vss | - | 5 | GND | |
| PA5 | 40 | Driver 4 | LED cathode | |
| PB0 | 24 | 1.8432 MHz osc. input | ||
| PB1 | 25 | !SHDN | - | |
| PB2 | 26 | 1.8432 MHz osc. enable | ||
| PB7 | 31 | EN | - | |