Caple C806C Manuál s instrukcemi stáhnout pdf (Strana 15)

PF2100

Modbus Card Instruction Manual v1.1

Jan 5, 2012

Page 11

Turn-Around Delay

RS-485 devices must tri-state when they are done transmitting on the bus in order to allow other devices to communicate. The amount of time required to

switch from transmit mode to tri-state or from receive mode to tri-state is called the turn-around delay. Different devices may have different turn-around

delays. It is therefore important to ensure that any two devices on the bus that must communicate with each other are setup to accommodate these delays.

Signal Naming Conventions

The RS-485 specification uses pins named “A” and “B” for the inverting and non-inverting pins respectively. Unfortunately, some vendors of RS-485 chips and

devices have named their pins reversed from the standard. The chipset used on the Modbus Card is one of those that uses the reversed naming convention.

This reversed convention was also used for the labels on the pluggable headers on Modbus Card v1.0. On the Modbus Card v2.0, the pluggable header uses the

less ambiguous polarity markings instead. It is therefore always important to consult the documentation for each RS-485 product on your bus to check which pin

is the inverting pin and which is the non-inverting pin. Below is a table showing various pin names that might be encountered on other products and

documentation.

Full-Duplex Wiring (Used on Modbus Card v1.0):

485

Names

Reversed

Names Polarity Names Description

RXD

Inverting Receiver Pin (Negative relative to other pin when idle)

RXD+

Non

Inverting Receiver Pin (Positive relative to other pin when idle)

n/a

TXD

Inverting Driver Pin (Negative relative to other pin when idle)

n/a

TXD+

Non

Inverting Driver Pin (Positive relative to other pin when idle)

Half-Duplex Wiring (Used on Modbus Card v2.0):

485

Names

Reversed

Names Polarity Names Description

“

” o

“

TXD

/RXD

”

Inverting Pin (Negative relative to other pin when idle)

“+” or “TXD+/RXD+”

Non

Inverting Pin (Positive relative to other pin when idle)

Common Ground

While the signalling over RS-485 is differential, it is still important to provide a common ground for all devices on the bus. If the difference between the ground

levels of any two devices on the bus exceeds -7/+12V, bit errors may be introduced or the devices may be physically damaged.

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 25 26

Komentáře k této Příručce

Žádné komentáře

Caple C806C Manuál s instrukcemi Strana 15

Komentáře k této Příručce

Související produkty a manuály pro Sporáky Caple C806C