Pico Communications E-14 - Manual (Page 14)

E‐14 Hardware Reference Manual www.picocomputing.com Pico Computing, Inc.
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*Please refer to the Analog Interface Selection Guide in Appendix E for compatible 8‐12‐bit converters
RS‐232 Serial Transceiver
The Pico E‐14 contains one asynchronous RS‐232 serial transceiver that also meets EIA/TIA‐232 and
V.28/V.24 specifications at a maximum data rate of 250kBps. Because the serial transceiver is directly
connected to the FPGA any bit high‐level protocol can be implemented in logic. Pico Computing
supports various asynchronous, synchronous and military serial protocols.
RS‐232 is the most common physical layer protocol for serial data. It is the standard used on serial mice
for computers, modems, consumer GPS receivers and even some military radios. Only one wire is
needed to send a signal on an RS‐232 link. A total of two devices are allowed on a single RS‐232 link.
In addition, there are two possible logic states on an RS‐232 line (high and low). The high voltage is
positive and the low voltage is negative.
Physical Layer Specifications:
Standard Noise
Immunity
Max
Distance
Max
Speed
Max
Connections
RS‐232 Satisfactory 50ft 250 kBps* 1 Tx / 1 Rx
*Maximum speed decreases with increased cable length.
*The old RS‐232, 422 and 485 standards are now obsolete and have been replaced by EIA/TIA‐232, 422
and 485.
Serial Transceiver Specifications:
Maximum Continuous Positive Input Voltage +25 VDC
Maximum Continuous Negative Input Voltage ‐25 VDC
ESD Protection Limit +/‐15,000V
Maximum Short Circuit Duration on Output Infinite
Typical RS‐232 Output Voltage +/‐ 5.4 V
RS‐232 Maximum Low Input Threshold* 1.2 V
RS‐232 Minimum High Input Threshold 1.5 V
*RS‐232 Receivers can accept digital inputs