Page 1 - Communications Configuration

Notes:

1. These are a mixture of read/write and write only registers (except on 72xx/73xx where registers 0-9 are read-only, not read/write).

2. The current slave address is fixed at 10 in the case of an RS232 link to a modem, or direct to a PC, since there is no point in changing a slave address on a 1 to 1 link. Address 10 was chosen so that that satellite 1 has slave address 1 etc. Register 0 specifies the current slave address in all other cases.

3. The site identity code is user definable and is used to identify a site.

4. The device identity code is user definable and is used to identify a device within a site.

5. 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.

6. 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.

7. 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. The enable flag for a socket that is not fitted will always be 0, any attempt to set it will be ignored.

8. 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.

9. 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.

10. The display unit connected to module indicates which type of unit is connected to the 8700. A zero value indicates there is no display unit connected and the module is locked.

 

Notes on passwords:

1. Passwords are intended to control access to control equipment via telemetry, they are not necessarily the same as passwords used to access the same equipment from a user interface. Such user interfaces are not defined in this standard in any way.

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. One of the 3 valid passwords 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 one of the 3 valid passwords 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 for a 1 minute lockout period, returning extended exception 8 (Inappropriate circumstances) at the third attempt (so it is immediately clear what has happened) and whenever a further attempt is made to enter a password during the lockout period. The password lockout period will double after every 3 unsuccessful attempts to enter a password, up to a maximum of 64 minutes, thus minimising 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 0. The count of invalid entries and the current lockout 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 them and then immediately re-establish the link.

8. When the link to a master is lost (a phone line is dropped or the master inactivity timer expires for example) the password status is set to 0 (invalid) or the highest disabled password level.

9. The ‘read only’ password is changed by writing the new value to register 34 and its ones-compliment to register 35 with a single function 16 (write multiple registers), any other operation will fail to change the password and return extended exception 7 (Illegal value written to register). The ‘control’ and ‘configure’ passwords are changed in the same way using the appropriate registers. The current ‘configure’ password must have been entered before any passwords can be changed.

10. If a password is changed to 0000 then that password level will be disabled, the password status will then default to the highest level that is disabled rather than 0 when an invalid password is entered, the password times out or the link to the master is lost. Even if one or more of the passwords has been changed to 0000, any attempt to write a password of 0000 to register 32 and 33 will be treated exactly as if an invalid password was entered.

11. A hub is intended to provide security for all its satellites using its own passwords, thus avoiding the complexity of managing passwords in every satellite separately, to facilitate this each satellite must have all its passwords disabled by setting them to 0000. If this is not done it is not possible to enter any password into a satellite unless the configure password is entered into the hub first, this is necessary to simplify the message filtering mechanism needed in the hub but is not a problem if the hub is used to provide security to the satellites as intended.

 

Registers

Register offset	Name	Minimum value	Maximum value	Scaling factor	Units	Bits/ sign	Read/write
0	Current slave address	1	247			16	Read/write
1	Site identity code	0	65534			16	Read/write
2	Device identity code	0	65534			16	Read/write
3	Baud rate	0	12			16	Read/write
4	Current language code	0	65534			16	Read/write
5	Unimplemented	0xFFFF	0xFFFF			16	Read only
6	Satellite socket 1 enable flag	0	1			16/16	Read/write
	Satellite socket 2 enable flag	0	1			15/16	Read/write
	Satellite socket 3 enable flag	0	1			14/16	Read/write
	Satellite socket 4 enable flag	0	1			13/16	Read/write
	Satellite socket 5 enable flag	0	1			12/16	Read/write
	Satellite socket 6 enable flag	0	1			11/16	Read/write
	Satellite socket 7 enable flag	0	1			10/16	Read/write
	Satellite socket 8 enable flag	0	1			9/16	Read/write
	Satellite socket 9 enable flag	0	1			8/16	Read/write
	Satellite socket 10 enable flag	0	1			7/16	Read/write
	Satellite socket 11 enable flag	0	1			6/16	Read/write
	Satellite socket 12 enable flag	0	1			5/16	Read/write
	Satellite socket 13 enable flag	0	1			4/16	Read/write
	Satellite socket 14 enable flag	0	1			3/16	Read/write
	Satellite socket 15 enable flag	0	1			2/16	Read/write
	Satellite socket 16 enable flag	0	1			1/16	Read/write
7	Satellite socket 17-32 enable flags	0	65535			16	Read/write
8	Master inactivity time-out, 0 means never time-out	0	36,000	0.1	Seconds	16	Read/write
9	Password time-out, 0 means never time-out	0	36,000	0.1	Seconds	16	Read/write
10-31	Reserved
32	Current password	0	9999	1		16	Write only
33	Compliment of current password	55536	65535	1		16	Write only
34	Set new read only password	0	9999	1		16	Write only
35	Compliment of new read only password	55536	65535	1		16	Write only
36	Set new control password	0	9999	1		16	Write only
37	Compliment of new control password	55536	65535	1		16	Write only
38	Set new configure password	0	9999	1		16	Write only
39	Compliment of new configure password	55536	65535	1		16	Write only
40	Display unit type connected to module	0	65535	1		16	Read only
41-255	Reserved

 

 

Baud rate

Code	Rate
0	110
1	150
2	300
3	600
4	1200
5	2400
6	4800
7	9600
8	14400
9	19200
10	28800
11	38400
12	57600
13	115200
14-99	Reserved

 

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