Basically S7 300 and all ET200 family remote I/O use the same
peripheral bus concept that was copied from S5 95/100 family.
Siemens added communication k-bus as well (MPI).
So if you open an 300 CPU (old one) you will see a
microcontroller C165, ASPC2 Profibus ASIC (DP versions CPUs)
and some flash/ram memory, RTC etc.
New ones are about the same thing but wafer form glued on
the same silicon.
CPU 300 runs PXROS OS from HighTec. The backplane bus consist on
15 pin wire spit bus where uper part is an asynchrony full duplex
serial communication line running at 5MHz that is P-BUS.
Logic behind the protocol is of course "proprietary" but
essentially is a multiplexed protocol that addresses master-slave
every card based on the slot number. It can be addressed up to 32 cards
(with IM module). It is capable to read/write P addresses
PIW/PQW or Data Records.
The lower part of connector is K-BUS (MPI) an RS485 running 187.5 Kbps.
=== Edited by Dec @ 8/4/2006 9:33 PM [GMT ] ===
=== Edited by Dec @ 8/4/2006 8:23 PM [GMT ] ===