55xGenComm1_29
26
GenComm Page 1 - Communications Settings
1. The current slave address is fixed at 10 in the case of an RS232 link to a modem, or direct to a
PC via the P810 interface.
2. The site identity code is user definable and is used to identify a site.
3. The device identity code is user definable and is used to identify a device within a site.
4. The meaning of the baud rate is shown in the table below, a slave device may not necessarily
support all baud rates, writing an unsupported value will return extended exception 7 (Illegal
value written to register) and will not change the Baud rate. Some systems may not allow the
Baud rate to be changed at all, it may be set by switches or from a user interface for example.
The baud rates available on a particular slave can be obtained by reading a register in the
communications status page.
5. The current language applies only to strings read by telemetry, it is quite separate from the
language selected for any user interface on the unit. The meaning of the code is defined in the
language codes section.
6. The satellite socket enable flags allow each satellite socket to be enabled or disabled, a socket
that is fitted but not in use must be disabled or the hub will think that the lack of response
indicates a problem and set the corresponding satellite error flag and telemetry alarm flag. Bit 1
corresponds to satellite 1 etc. The enable flag for a socket that is not fitted will always be 0, any
attempt to set it will be ignored.
7. The master inactivity time-out is used to detect the loss of communication from the master, if a
query is not received for this period the slave device assumes the link to the master has been
lost. The link is assumed to have been established as soon as a query arrives from the master.
8. The password time-out is used to disable the password automatically, if a valid password is not
written for this period the password status will be set to 0 (invalid) or the highest disabled
password level.
Notes on passwords
1. Passwords are intended to control access to control equipment via telemetry.
2. Passwords are 4 digit numbers similar to ‘PIN numbers’ which are widely accepted and easier
to enter via a limited user interface than alphanumeric strings.
3. The password is written into register 32 and its ones-compliment written into register 33 with a
single function 16 (write multiple registers) to set the current password status.
4. The password status in the communications status information page indicates which level of
access has been granted, when the password times out the status becomes 0 (invalid) or the
highest disabled password level.
5. Entering a password that does not match the valid password will cause the password status to
be set to 0 (invalid) or the highest disabled password level and return extended exception 7
(Illegal value written to register)
6. The password status can be cleared to 0 (invalid) or the highest disabled password level either
by writing a password that is known to be invalid or by writing any value to register 32 without
writing to register 33.
7. If an invalid password is entered 3 times the slave device will then reject any further attempt to
enter a password (including a correct password) for 1 minute, returning extended exception 8
(Inappropriate circumstances). After this period, three further attempts at sending the correct
password will be allowed, after which time, further attempts to enter a password (including a
correct password) will be inhibited for two minutes. This period will double after every three
unsuccessful attempts to enter a password, up to a maximum of 64 minutes. This minimises the
risk of a deliberate attack being able to find a valid password. When a valid password is entered,
the count of invalid entries will be reset to zero. This timer will not be reset by loss of the
communication link as it would be possible for an attacker to drop the link to reset the timer then
immediately re-establish the link.
8. When the link to a master is lost (a telephone line is dropped or the master inactivity timer
expires for example) the password status is set to zero (invalid) or the highest disabled
password level.
9. The password is changed by writing the new value to register 38 and its ones-compliment to
register 39 with a single function 16 (write multiple registers). Any other operation will fail to
change the password and will return extended exception 7 (Illegal value written to register). The
current password must have been entered before any passwords can be changed.
To Next Page
Loading...
