Host Interface
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COM-C | Communication Module
DOC021001DG12EN | Revision 12 | English | 2011-06 | Released | Public
© Hilscher, 2002-2011
3.4
Signals of the Host Interface
3.4.1
Power Supply of the COM-C Modules
Only a single 3.3 V operation voltage is needed for the COM-C Module. The voltage must be regu-
lated and can have a tolerance of ±5% (3.1 - 3.5 Volt) and must be connected twice to the system
bus connector X1. To avoid EMI problems we suggested using bypass capacitors in the power
supply path. All other special voltages required on the COM-C Module are generated by on board
DC/DC converter.
A watchdog circuit on all COM-C Modules supervises the voltage and the microprocessor. If the
voltage falls below the voltage reset level of typically 2.93 V (2.85 - 3.00 V) the COM-C are hold in
reset state. If the voltage increases over the reset voltage level the COM-C Module begin with the
power up sequence. To avoid problems with the power supply we recommended using a voltage of
3.3 V. So the operation will be in the safe range of voltage operation area and short voltage drops,
spikes and noise will not produce any reset conditions.
3.4.2 RESET
Signal
It is possible to reset the COM-C Module by the extra reset signal RES#. For operation of the
COM-C Modules it is important to switch the signal RES# to high level. Then the COM-C Modules
begins with the program execution and initialization. This power up time is different for each COM-
C Module. Normally, the time is about less than two seconds. The COM-C Module is in reset state
when the signal RES# has a static low level. To reset the COM-C Module the RES# signal must be
low for more than 10 µs.
Note
During Reset all signals of the Dual-port memory are configured as inputs! The output
level could be floating. If the host system needs a stable level a pull-up or pull-down re-
sistor is required on the host board.
3.4.3
The Dual-port Memory Bus of COM
The communication for all input and output data and control commands between the COM-C Mod-
ule and the host system are exchanged over the dual port memory with the same memory address
map. The highest 1 KByte is reserved for the communication mailboxes and some control and pa-
rameter values. The rest of the Dual-port memory is divided into two data areas, an input and out-
put process data. Please refer at the special documents of the data model and communication
methods.
From host system side, the Dual-port memory looks like static RAM. The COM-C Modules have
always an 8 KByte Dual-port memory even if the firmware doesn't need so much memory. Only a
few signals are used to control the access to the Dual-port memory.
The maximum driving capability for the data lines is 4 mA.
To avoid data loss through simultaneous access at the same memory cell, it is necessary to use
the BUSY# signal.
