The only way to make a cable resistant to higher temperatures (while keeping its mechanical properties somewhat normal) is by using heat-resistant plastics such as Silicone rubber or Teflon (PTFE). Note that PTFE is not halogen-free and Silicone seems to pose other health risks when on fire (ultimately is combustible, hard to extinguish, and develops a lot of nasty smoke when burning). A popular way of making cables last longer when on fire is by adding layers of "armor" (a steel sleeve and more insulation) - mechanically, those are a completely different category of cables. This is allright for basic applications (low transfer rate) and may actually mean longer reach (less DC resistance), as the lower RF Z typically means thicker conductors compared to insulation thickness (distance of conductors in the pair). The result was somewhat surprising: the wobble has actually increased a bit, compared to the previously unbiased delta terminator. At higher baud rates though, the lower Z means attenuation at the transmitter, compared to a proper 120 Ω cable (which translates into shorter reach). There are however lower-grade "fire-resistant" cables matching the general "shielded twisted pair" specification, for basic signaling applications, which can also be used for RS485 for shorter distances.

The basic resistive-only termination of the common-mode component would increase stress on the drivers (heat dissipation), and would hamper attempts at DC biasing (details of which will be discussed below). This is not external biasing resistors, but a receiver characteristic of limiting induced differential noise due to imbalance of the inputs. The first function is to attenuate large signals that are beyond the range of the supply voltage of the receiver. This stopped the data flow to the receiving end, allowing the receiver to process the data in its buffer. The processor could check the level of the buffer and only had to stop the data when the buffer was too full. Transmitting data bidirectionally over the same wire(s), rather than unidirectional transmission, requires a turn-around delay. The other is that the IC manufacturer's datasheets never state that the IC pin A is the same thing as RS-485's wire "A".

The pair should actually be accompanied by at least a separate ground conductor in the same sheath, RS485 standard because a reference ground is almost mandatory and a tightly aligned conductor means low loop inductance (see above). 2 and 3 in the table of waveforms above (use the schematics in table header as a guide). If you have a nice-looking shielded twisted cable that doesn't have its impedance stated, you can find out yourselfs (see my reflectoprobe suggestions above) - you will likely measure something between 60 and 80 Ω diff-mode, and consequently 15-20 Ω common mode. Quality STP cables for high-performace communications tend to have the nominal impedance stated in the datasheet (meaning the diff-mode impedance), often along with attenuation values in dB for a few radio frequencies. For RS485, the impedance of just 70 Ω may prove a tad too low for longer distances. Grounds between buildings may vary by a small voltage, but with very low impedance and hence the possibility of catastrophic currents - enough to melt signal cables, PCB traces, and transceiver devices.

First of all I verified, that the RS485 transceiver is essentially alive, that both TX and RX work (using another converter). Biasing has a number of uses on a RS-485 network, but first lets look at what RS422 and RS-485 have to say. In a RS-485 cable, data typically flows in both directions along any particular wire, sometimes from the "A" of the first device to the "A" of the second device, and at a later time from the "A" of the second device to the "A" of the first device. Just because a protocol is used with a particular implementation of RS-232 or RS-485, does not mean it is part of the standard. It does not mean that this protocol is part of the standards or that only this protocol may be used with the 232/422/485 standards. RS232 was developed in the 1960s, and among other things, specified an electrical standard, a protocol standard, handshaking, and connector pin-out. The connector resides in layer one of the OSI model and RS-232 includes the connector.