3
1.1 Overview
A schematic diagram of the Universal Serial Interface is shown in Figure 1.1 and a connection
diagram is shown in Figure 1.2.
The USI features three switches: The USI Function switch, the Data I/O switch, and the
Data Handshake switch.
The Function switch is located at the top of the USI and has three settings: UPLOAD,
NORMAL, and Y-CABLE and operates as follows:
UPLOAD connects the AT-AUTO(tm)directly to the PC’s RS-232 serial port and elec-
trically isolates them from the radio’s serial data port, permitting the user to upload new
AT-AUTO(tm)firmware without the need to physically remove any of the serial data cables.
NORMAL connects the AT-AUTO(tm)directly to the radio’s RS-232 serial port and elec-
trically isolates them from the PC’s serial data port, enabling the AT-AUTO(tm)to directly
query and follow changes in the radio’s operating frequency.
Y-CABLE connects the PC’s serial port directly to the radio’s RS-232 serial port and also
connects the AT-AUTO’s(tm)serial data receive line. In this setting the PC is able to directly
control the radio via the radio’s serial data port, and enables the AT-AUTO(tm)to intercept
serial data sent from the radio to the PC, permitting it to automatically follow changes in
the radio’s operating frequency.
The USI Data I/O switch is located below and to the left of the Function switch. This
switch is enables electrically swapping the serial data transmit and serial data receive pins
for those radios that do so. Place this switch to the REVERSE position when attempting
to use a radio with swapped data pins.
The USI Data Handshake switch is located below and to the right of the Function
switch. This switch has two positions labled PC-RIG,INT. The AT-AUTO(tm)does not
employ serial data handshaking, however some radios will not respond to any commands
unless the radio’s cleared-to-send (CTS) input is asserted. Placing this switch to the INT
(internal) position will electrically connect the radio’s request-to-send (RTS) output directly
to the radio’s CTS input and thereby enable the radio to send serial data (if waiting for CTS
to be asserted). This is the “normal” recommended position. Setting the Data Handshake
switch to PC-RIG, enables RTS/CTS control between the PC and the radio.
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