[Ham-Mac] USB Serial adapters

[Chris Smolinski]

>Hi Chris,
>
>On 23-Jun-05, at 7:50 AM, Chris Smolinski wrote:
>
>>I have both adapters. The advantage of the high speed unit is it 
>>has a standard PC 9 pin serial port connector, with the extra 
>>handshake lines.
>
>Just to clarify - the Twin serial adapter includes the same DTR and 
>RTS handshake lines as the high speed - it's just that the data and 
>handshake lines are balanced in RS-422.

Here is the 8 pin Mac serial port pinout, there is only ONE output 
handshake line:

1 Output Handshake
2 Input Handshake
3 TxD-
4 GND
5 RxD-
6 TxD+
7 GPi
8 RxD+


vs the PC 9 pin serial port:

1 CD    carrier detect
2 RD    receive data
3 TD    transmit data
4 DTR   data terminal ready
5 GND
6 DSR   data set ready
7 RTS   request to send
8 CTS   clear to send
9 RI    ring indicator

Which  has two output and two input handshake lines (three if you count CD)


>
>>I believe the voltage levels are higher as well, +/-12 volts not 
>>+/-5 volts like Mac style serial ports.
>
>Part of the confusion is that both standards specify a voltage range 
>rather than an absolute voltage.
>In practice the RS-422 driver chip manufacturers usually provided 
>+-6v for the differential lines...

The problem is that some PC devices (like the early RigBlasters, 
maybe even the current ones?) were not happy wiith the +/- 5 volt 
output from a Mac serial port, they expected the +/- 12 volt outputs 
common on PCs.
-- 

---
Chris Smolinski
Black Cat Systems
http://www.blackcatsystems.com