Pocket Computing @ WRL

Host-computer connection


     
 

Itsy v1 and v2 systems can be connected to a host computer through the supplied input/output (I/O) connector. The Itsy v1 I/O connector features input power and an RS-232 link. The Itsy v2 I/O connector also offers a USB client port. Note that Itsy units shipped to sites in the USA will be shipped with power supplies intended to be used to power the unit; those users located outside of the USA will have to locate their own power supplies.

Itsy v1 input/output cable

Itsy v1 is typically used (and shipped) with a special Y-shaped I/O cable. This cable connects to an Itsy on one side and has a barrel-shaped power connector and an RS-232 MMJ connector on the other side.

The input power is directly connected to the batteries and, therefore, should never be used with the batteries in place. The voltage range is 2.0 V to 3.3 V. The positive side is the inside connection of the barrel connector and the negative side is the outside connection.

The RS-232 link corresponds to a null-modem cable. Therefore the MMJ pinout is that of a DTE (see below).

Itsy v2 docking adaptor

Itsy v2 is typically used (and shipped) with a docking adaptor. This adaptor connects to an Itsy with an I/O cable and offers standard power, RS-232, and USB connectors.

The input power connector is a barrel connector, used to recharge the Itsy's Li-ion battery. Although the voltage range is 3.5 V to 13 V, the battery cannot be fully charged if the voltage is less than 4.5 V. Also, to avoid excessive heat dissipation, it is better to avoid applying voltages higher than 7 V - 8 V for long periods of time. The positive side is the inside connection of the barrel connector and the negative side is the outside connection. A jumper is used to select the power source between this connector and the USB connector.

Two RS-232 connectors, a 9-pin DIN connector (DB-9) and a 6-pin MMJ connector, are provided for the same serial port. Therefore, only one of these connectors should be used at any time. Both are wired as a DTE (see below)

The USB connector is the standard USB client connector.

Itsy v2 modem

The Itsy modem is an analog dial-up modem (up to 56 Kb/s) that connects to an Itsy with a similar I/O cable. It has a power connector and an RJ-11 phone connector.

The input power connector is identical to that of the Itsy docking adaptor (see above). However, since it is also used to power the 5 V modem, the voltage should be higher than 5 V.

Serial connector standards

Several different types of connectors are used for RS-232 serial ports. These include 25-pin and 9-pin DIN connectors (DB-25 and DB-9). The following table gives the pinout for DB-25 and DB-9 connectors:

| Name   | Src. | Dst. | Description               | DB-25 | DB-9  |
+--------+------+------+---------------------------+-------+-------+
| FG     |      |      | Frame (chassis) Ground    |   1   |       |
| TxD    | DTE  | DCE  | Transmitted Data          |   2   |   3   |
| RxD    | DCE  | DTE  | Received Data             |   3   |   2   |
| RTS    | DTE  | DCE  | Request To Send           |   4   |   7   |
| CTS    | DCE  | DTE  | Clear To Send             |   5   |   8   |
| DSR    | DCE  | DTE  | Data Set Ready            |   6   |   6   |
| SG     |      |      | Signal Ground             |   7   |   5   |
| DCD    | DCE  | DTE  | Data Carrier Detect       |   8   |   1   |
|        | DCE  | DTE  | Positive DC test voltage  |   9   |       |
|        | DCE  | DTE  | Negative DC test voltage  |  10   |       |
| QM     | DCE  | DTE  | Equalizer Mode            |  11   |       |
| (S)DCD | DCE  | DTE  | Sec. Data Carrier Detect  |  12   |       |
| (S)CTS | DCE  | DTE  | Sec. Clear to Send        |  13   |       |
| (S)TxD | DTE  | DCE  | Sec. Transmitted Data     |  14   |       |
| TC     | DCE  | DTE  | Transmitter Clock         |  15   |       |
| (S)RxD | DCE  | DTE  | Sec. Received Data        |  16   |       |
| RC     | DCE  | DTE  | Receiver Clock            |  17   |       |
|        |      |      | Unassigned                |  18   |       |
| (S)RTS | DTE  | DCE  | Sec. Request To Send      |  19   |       |
| DTR    | DTE  | DCE  | Data Terminal Ready       |  20   |   4   |
| SQ     | DCE  | DTE  | Signal Quality detect     |  21   |       |
| RI     | DCE  | DTE  | Ring Indicator            |  22   |   9   |
|        | DTE  | DCE  | Data signal rate selector |  23   |       |
| (TC)   | DTE  | DCE  | Ext. Transmitter Clock    |  24   |       |
|        |      |      | Unassigned                |  25   |       |
+--------+------+------+---------------------------+-------+-------+

DTE: Data Terminal Equipment (computer)
DCE: Data Communication Equipment (modem)
      

6-pin MMJ connectors are also sometimes used. When differential signals are not used, TX- and RX- are set to GND. The following table gives the pinout for MMJ connectors:

|        |      |      |                           | 6 MMJ | 6 MMJ |
| Name   | Src. | Dst. | Description               |  DTE  |  DCE  |
+--------+------+------+---------------------------+-------+-------+
| DTR    | DTE  | DCE  | Data Terminal Ready       |   1   |   6   |
| TX+    | DTE  | DCE  | Transmitted data +        |   2   |   5   |
| TX-    | DTE  | DCE  | Transmitted data - (GND)  |   3   |   4   |
| RX-    | DCE  | DTE  | Received data - (GND)     |   4   |   3   |
| RX+    | DCE  | DTE  | Received data +           |   5   |   2   |
| DSR    | DCE  | DTE  | Data Set Ready            |   6   |   1   |
+--------+------+------+---------------------------+-------+-------+

DTE: Data Terminal Equipment (computer)
DCE: Data Communication Equipment (modem)
      

An adaptor can be used to convert a DTE MMJ plug into a DB-9 connector. The Digital/Compaq part number is: H8571-J REV A or REV B. This adaptor implements:

6 MMJ                        DB-9 (female)

                     ------  1  DCD
                     |
                  ---+-----  2  RxD
                  |  |
DTR  1  -----\ /--+--+-----  3  TxD
              X   |  |
TxD  2  -----/ \--+--+-----  4  DTR
                  |  |
GND  3  ------*---+--+-----  5  SG (GND)
              |   |  |
GND  4  -------   |  *-----  6  DSR
                  |  |
RxD  5  -----------  |       7  RTS
                     |
DSR  6  -------------*-----  8  CTS

                             9  RI
      

The Itsy Project is a joint effort of the Western Research Lab and the Systems Research Center

Last update: October 1998