Having to mobilise equipment in a short time , with limited equipment & space it is sometimes necessary to use Rs232 to USB serial converters. But the inherent latency is not ideal for a survey setup.
When data is sent from a serial device to a USB converter it is cached on the USB converter until one of two things happens:
- Transfer size – More then x BYTES are collected or
- Latency timer – More then n Milliseconds (ms) expirer.
Luckily we can set the Transfer size, and latency timer.
Most USB to 485 devices that I have used have the ability to set the transfer size and the latency timer.
- Start menu–> Settings –> Control panel –> device manager –> Ports (COM & LPT) –>{Select your USB to RS485 converter}
- Right click and select “Properties”
- Select the “Port Settings” tab
- Click the “Advanced” button
- Change the Latency Timer (mSec) to 1ms or the lowest possible setting (I use 4ms).
- Change the USB Transfer sizes to 256 - the largest NMEA data string is 82 bytes.
- Save and close.
