Note:

Serial Interface Contacts

  PCPD (Rear View)               Cradle (Front View)

10 9 8 7 6 5 4 3 2 1             1 2 3 4 5 6 7 8 9 10
 | | | | | | | | | +->   DTR   <-+ | | | | | | | | | 
 | | | | | | | | +---> +3.3VDC <---+ | | | | | | | |
 | | | | | | | +----->   RD    <-----+ | | | | | | |
 | | | | | | +------->   RTS   <-------+ | | | | | |
 | | | | | +--------->   TD    <---------+ | | | | |
 | | | | +----------->   CTS   <-----------+ | | | |
 | | | +------------->  GPI 1  <-------------+ | | |
 | | +--------------->  GPI 2  <---------------+ | |
 | +----------------->  unused <-----------------+ |
 +------------------->   SG    <-------------------+

Pin #	Signal Name (Direction)	Function
1	DTR (out)	Non-standard implementation. Signal is named RS232_V+. This is the voltage doubler output from the RS232 transceiver's V+ pin (pin 3) through a 330 ohm resistor. It is used as the Data Terminal Ready (DTR) signal. When the serial port is "opened" by Serial Manager, it enables the RS232 transceiver and the UART. As long as the transceiver is enabled this pin outputs an asserted signal. The signal is 3.0 volts when the transceiver is shut down (normal mode) and is about 6.0 volts when the transceiver is enabled (HotSync). When this signal is at 6.0 volts it is a valid RS232 assertion. Note: According to specifications, a 3.0 volt signal constitutes a valid RS232 assertion, but it "seems" as the time that all pocket modems which require DTR to be valid simply have a logic detector to detect the signal being greater than 4 volts. So, effectively 3 volts is not a valid assertion and that is why this simple implementation works.
2	VCC (out)	This is tied to Vcc (3.3v) through a 330 ohm resistor. This signal is connected to the HotSync button (normally open) on both the cradle and the Palm Modem. The other side of the HotSync button connects to pin 7 (GPI1).
3	RD (in)	Receive Data -- from PC to PCPD
4	RTS (out)	Request To Send -- hardware flow control handshake signal (from PCPD)
5	TD (out)	Transmit Data -- from PCPD to PC
6	CTS (in)	Clear To Send -- hardware flow control handshake signal (from PC)
7	GPI1 (in)	Interrupt line for initiating HotSync. This input requires a voltage greater than about 0.7 volts in order to turn on a MUN2214 NPN transistor which asserts a low on the DragonBall UART IRQ1 (U1 pin 38).
8	GPI2	Peripheral ID line (for HotSync). Signals "Modem HotSync" when asserted high (this is achieved in the Palm Modem because this pin is connected to pin2 through a 20K ohm resistor). This input requires a voltage greater than about 0.7 volts in order to turn on a MUN2214 NPN transistor which asserts a low on the DragonBall UART GPIO (U1 pin 32) to present a "modem connected" ID signal to the processor.
9	Unused	(Reserved)
10	SG	Signal ground.

Notes:

• Looking at the back of the PCPD the pins are counted 1 to 10 from right to left.
• We use RTS and CTS to communicate at speeds over 2400 bits per second.
• The DTR signal is not a standard implementation. It is important because some modems will not function without it and have no override. We found that this is particularly true with modems sold in Europe.
• All PCPDs released so far do not implement DSR (Data Set Ready), RI (RIng detect), CD (Carrier Detect), and TC (Transmitter Clock).
• No TC (Transmitter Clock) means that synchronous transmission is not possible.
• Transceivers used:
  Pilot 1000/5000 -- Maxium MAX3222
  PalmPilot Personal/Professional -- Sipex SP385ACA, Linear Technology LTC1385CG
  Palm III -- Sipex SP385ACA

Palm/3COM 5-12-98
(minor modifications by Jason White)

Palm Cradle to DB-9F Serial Wiring Diagram

 PCPD/Cradle    DB-9F
 -----------    -----   
    (DTR) 1 ----- 6 (DSR)
(+3.3VDC) 2 ---------------+
     (RD) 3 ----- 3 (TD)   |
    (RTS) 4 ----- 8 (CTS)  o|_ HotSync
     (TD) 5 ----- 2 (RD)   o|  Button
    (CTS) 6 ----- 7 (RTS)  |
   (GPI1) 7 ---------------+
   (GPI2) 8 Unused
          9 Unused
    (SG) 10 ----- 5 (SG)