VIPA CP 240 RS232, Manual

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Chapter 6 CP 240 - M-Bus Manual VIPA System 200V
6-6 HB97E - CP - Rev. 11/30
Communication principle
The CPU writes data via the back plane bus, which is to be sent into the
according data channel.
The communication processor enters them into a ring buffer (2048Byte)
and transmits them via M-Bus.
When the communication processor receives data via M-Bus, the data is
stored in a ring buffer (2048Byte). The received data may now be read
telegram by telegram from the CPU via the data channel.
The exchange of received telegrams via the back plane bus happens
asynchronously. When a complete telegram has been arrived via M-Bus, it
is stored in the buffer. The user data are extracted from the M-Bus
telegram and transferred to the CPU via back plane bus.
A telegram that is to send has to be transferred to the CP 240. This
recognizes the telegram type due to the length definition, supplements it
with the according telegram bytes and handles the telegram on to the send
buffer. The CP 240 compiles these blocks in the send buffer and sends it
via M-Bus with the specified baud rate as soon as the telegram is
complete. Since the data transfer via back plane bus happens
asynchronously, a "software handshake" is used between CP 240 and
CPU. The registers for the data transfer from the CP 240 have a width of
16Byte. For the handshake, the Bytes 0 to 3 (word 0 and 2) are reserved.
The following picture shall illustrate this:
V-Bus
SEND
OUT
IN
Byte n
. . .
Bte4
Byte 2/3
Byte 0/1
Byte n
. . .
Byte 2/3
Byte 0/1
Byte 4
Byte 4
Soft handshake via Byte 0 ... 3
TxD Cnt
RxD Cnt
TxD Cnt
RxD Cnt
Communications processor
REC
SEND
REC
Baud rate
user data
Re
user data Re
telegram
Baud rate +
telegramm
M-Bus
Telegram
Telegram
MC
Baud rate
Send and receive
data
Communication
via back plane bus
Tasks of the CPU