SECS-I Details

The AdeptGEM SECS-I software is in compliance with the protocols defined in "SEMI E4: SEMI Equipment Communications Standard 1, Message Transfer (SECS-I)." Section 7.2.4 of that standard, "Interleaving Messages", which is optional, is not implemented.

SECS-I Parameters

There are several parameters that can be set to influence the behavior of the AdeptGEM programs that implement the SECS-I communication layer. The SECS-I parameters are defined in the SEMI specification and are presented here. In some cases, the setting of these parameters will be obvious, based on the physical equipment. (The BAUD rate, for example, is limited by the capabilities of the equipment at either end of the communication link.) Other parameters will need to be determined based on the behavior of the equipment in the host environment. The Retry and T4 parameters, for example, do not have an intrinsic "correct" value, but depend on the acceptable behavior of the entire system.

All the SECS-I parameters are stored as equipment constants in the GEM Variables database (see SECS-I Communication Parameters and Predefined Collection Events). The GEM Variable database can be accessed with the menu selection:

Edit -> GEM Variables

The following table shows the range, default, and resolution for each parameter (T1 through T4 values are in seconds):

Table 4-1. SECS-I Communication Parameters
Parameter
ECID
Default
Min
Max
Resolution
BAUD
9152
9600
110
38400
See FSET instruction1
DEVID
9151
4660
0
32767
1
T1
9106
0.5
0.1
10
0.016
T2
9107
10
0.2
25
0.016
T3
9108
45
1
120
1
T4
9109
45
1
120
1
RTY
9115
3
0
31
1
M/S

Always set to equipment.2
1. The baud rate specified in the GEM Variables database can be different from the rate that is configured in the V+ system configuration data. The AdeptGEM system automatically sets the baud rate to that specified in the GEM Variables database.
2See the global variable gm.secs1.master for more information about this parameter.

Other SECS-I Requirements

1. Duplicate block detection is optional and is set up with equipment constant ID 9116 in the GEM Variables database. By default, it is enabled.

2. Expected delays under normal operating conditions:
Parameter
Definition
Delay
T1
Intercharacter timeout
10/Baud rate
T2
Protocol timeout
0.032
T3
Reply timeout
Depends on system configuration (typically 10-30 seconds)
T4
Interblock timeout
Depends on system configuration (typically 1-2 seconds

3. Multi-block messages are supported for both sending and receiving.

4. The maximum received message size is configurable using ECID 9154 in the GEM Variables database. The absolute maximum size is 64 KB (65,535 bytes). (The SECS-II layer may impose limits on the size of many messages.)

5. Message interleaving is supported.

6. Only one device ID is supported per CPU (set with equipment constant 9151 in the GEM Variables database).

7. Only one transaction is processed at a time. (If a message is received from the host while a previous message is being processed, the new message is buffered for processing later. Up to 100 pending messages can be buffered in this way.)