Differences between cm-a and cm-2 interfaces, Connection status detection, Cm-2 module interface connectors – Cirrus Logic AN335 User Manual
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10.DIFFERENCES BETWEEN CM-A AND CM-2 INTERFACES
Detailed information on the points referred to here are available in the CobraNet Programmer's Reference Manual
and the CobraNet Hardware User's Guide available for download at
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There is an additional address line on the CM-2. See schematic for connector pin out. This line should al-
ways be driven or tied low. The CM-2 module contains a pull-down resistor on this pin allowing it to be left
unconnected.
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CM-2 uses a single 3.3V supply. It does not use 5V. If a 5V supply exists on the connector it can be left in
place in order to gain an additional AC return path.
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Placement of bypass caps on the supply lines close to the connector is recommended, even on the unused
5V line.
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Four of the serial I/O (SSI) lines (see CM-2 schematic) have pull-up / pull-down resistors used by the pro-
cessor to determine the boot mode. If you have pull-ups / pull-downs on the host side of the connector to
terminate unused SSI lines, make sure the values are high (> 50k Ohm) so they do not overpower the on-
board resistors.
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The HMI interface differs. There is a code example in the Hardware User's Guide which illustrates how to
auto-detect presence of a CM-1 or CM-2. This code can be used to determine module type and appropriate
interface protocol to use. There are also examples showing how to properly use the CM-2 interface. The
most significant command change involves use of the Translate Address and Goto Address commands rec-
ommended in lieu of the Set Address command.
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Polarity of HREQ changes on chips and CM-2 modules depending on transfer direction.
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The HMI interface on CM-2 and chips is 32 bits wide, but most data is still contained within a 24-bit window
of that 32 bits. There are some exceptions. Please refer to the Programmer's Reference and Hardware Man-
ual for possible changes to variables that will be used. The MSB must be nulled, if not used.
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The setup and hold timing has changed between the modules. This could be an issue, if the processor con-
nected to the HMI features high speed interfaces. Please review the timing diagrams in the Hardware's Us-
er's Manual to insure HMI interface timing compliance.
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The same Flash memory type is used for CM-1 and CM-2 modules.
11.CONNECTION STATUS DETECTION
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Detection of the current connection status of CobraNet nodes can be easily accomplished by reading MIB-
variables.
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An array variable called ifmtStatus provides the current connection status and one variable exists for each
Ethernet interface. It can be accessed via SNMP or as an HMI variable.
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During normal operation, ifmtStatus will show a value of 0x07. At least, it should show 0x03 if the link is
present as a full duplex connection.
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Please refer to page 118 of the Programmer's Reference Manual version DS651PM25 for information on
this variable.
12.CM-2 MODULE INTERFACE CONNECTORS
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The mating connectors for the CM-2 modules are manufactured by Samtec, type SQW-120-01-L-D-VS-A.
Please refer to
details and ordering samples.