USB Interfaces User’s Guide
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For some operating systems you need to install a driver; others automatically use a common class driver. See
COM Port
Emulation Driver
on page 1-4 for further information.
Scan the following bar code to program the imager for a COM port interface.
Hardware and Software Flow Control
USB has built in flow control, so there is no need to simulate any flow control. The (Windows) driver ignores any flow control
setting.
Hardware Flow Control
If you turn on RTS/CTS mode in the device, it raises its RTS output before sending any data. The device also monitors its CTS
input before sending a block of data (a scanned bar code). There is no check for this “line” on a character-by-character basis.
Note: An asterisk (*) denotes the default setting.
Software Flow Control
The device supports two modes of software flow control:
Xon/Xoff: Not supported by this interface
ACK/NAK: Works as expected (including a resend if you respond with NAK)
Note: An asterisk (*) denotes the default setting.
Baud Rate, Data Bits, Stop Bits, and Parity
Baud rate, number of data and stop bits, and parity are important settings for any RS-232 connection, however they are
unnecessary with this interface. USB has its own transfer parameters and is much safer than a regular RS-232 connection.
There is no need for error detection on the application level. If your application sets these parameters, they are ignored.
Response Timing
USB transfers data in blocks, using 1millisecond frames. This has some influence on turnaround time and minimum character
transfer time. If just a single character is sent it might take up to a few milliseconds to arrive - the same amount of time it takes
to send several kilobytes.
Transfer Speed
COM port emulation is much faster than a regular COM port. The speed varies depending on operating system, drivers, and
other devices connected to the same bus. On a Macintosh you can expect about 640 Kbit/sec. Windows systems can reach
more than 7 Mbit/sec with custom serial COM port emulation drivers. This type of driver is available at
www.handheld.com
.
