ICS ELECTRONICS 9099, Инструкция по эксплуатации

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4.3 bLOCK DIAGRAM DESCRIPTION
Figure 4-2 shows a block diagram of the 9099’s internal logic. The 9099 is made
up of seven major elements, most of which are interconnected to the ARM9
microprocessor by a common data, address and control signal bus.
Incoming network messages are received by the LAN Interface chip. The
LAN Interface chip transfers the decoded data to the ARM9 microprocessor
when it receives a message. Depending upon the message type, command
characters are parsed and used to change/query the 9099’s operational settings
or to transfer data to or from the Serial Interface. Modbus TCP/IP packets are
directly converted to Modbus RTU packets.
The 9099’s Serial Interface has several UARTs, two of which are connected
to the RS-232 and RS-485 transceivers. A separate RS-232 Enable jumper
selects the active UART. The RS-232 transceiver produces or receives the
RS-232 single ended, bipolar signals. Typical RS-232 output levels are ± 8
Vdc. Minimum input levels are ±5 Vdc. The RS-485 transceiver generates
and receives differential RS-485 signals. The RS-485 driver has more drive
capability than the older RS-422 drivers but it makes the same signal levels
and thus the interface is RS-422 and RS-485 compatible. The two pairs of
signals can be used as a 4-wire differential interface or jumpered internally to
form a 2-wire RS-485 signal pair. The Rx signal pair can also be jumpered
to an internal termination network that provides a pull-up, termination and
pull-down resistors. For 2-wire operation, the HD/FD jumper is set to HD and
the 9099’s RS485 parameter is set ON so the 9099 will not drive the RS-485
network when it is not transmitting a message.
Incoming serial data from the Modbus slave device is received, converted into
TTL levels by the appropriate transceiver chip and applied to the UART in the
ARM9 microprocessor. The received RTU packet is then checked for a valid
CRC termination. If the received packet is valid, any data in the received mes-
sage is converted into the correct format and placed in the output buffer where
the data can be transferred out when the client requests them (analogous when
a GPIB device is addressed to talk) Messages that contain errors or Exception
messages cause the 9099 to set bits in the Questionable Register and to place
an error value in the Modbus Error Register. Modbus TCP/IP responses are
formatted into a Modbus TCP/IP packet and transmitted back to the Modbus
master.
The 9099 contains a multilevel Status Byte Register and Event Register struc-
ture for each interface which enables the 9099 to generate a Service Request
when errors are detected.