FC 98 - Slave Select

The slave select function code monitors a pair of redundant I/O module function blocks. Specification S9 is a toggle input that switches from one module to the other when both modules are good.

 

The block has two outputs, select (N) and interlock (N+1). The select output identifies the active module, and the interlock indicates when both modules are bad.

 

Outputs:

Blk

Type

Description

N

B

Module selected:

0 = module 1

1 = module 2

Initial value is zero. Value changes only if the active module is bad and the inactive module is good, or if both modules are good and the toggle input makes a 0 to 1 transition.

N+1

B

Interlock:

0 = one or both modules good

1 = both modules bad

 

 

 

Specifications:

Spec

Tune

Default

Type

Range

Description

S1

N

0

I

Note 1

Block address of boolean status for module 1

S2

N

0

I

Note 1

Block address of boolean status for module 1

S3

N

0

I

Note 1

Block address of I/O, boolean or real with quality, for module 1

S4

N

0

I

Note 1

Block address of I/O, boolean or real with quality, for module 1

S5

N

0

I

Note 1

Block address of boolean status for module 2

S6

N

0

I

Note 1

Block address of boolean status for module 2

S7

N

0

I

Note 1

Block address of I/O, boolean or real with quality, for module 2

S8

N

0

I

Note 1

Block address of I/O, boolean or real with quality, for module 2

S9

N

0

I

Note 1

Block address of toggle input (if both modules are good, a 0 to 1 transition on this input changes state of the select output)

 

NOTE:

1. Maximum values are: 9,998 for the BRC-100, IMMFP11/12 and 31,998 for the HAC

 

 

98.1 Specifications

 

S1 - STTSA1

Block address of the boolean status for module one. Each module has a status associated with it that defines if the I/O carried by the module is valid. Function codes 79 and 83 provide the module status outputs.

 

S2 - STTSB1

Block address of the boolean status for module one. There are two status specifications for each module because IMDSO14 handles two groups of eight outputs. Function code 83 provides the status on groups of eight points only. Therefore, if redundant modules are to be monitored, there must be a function code 83 block configured for each group of eight outputs. A similar configuration exists for IMDSI12, IMDSI13, IMDSI14, IMDSI15, and IMDSI22 modules used for inputs. If either <S1> or <S2> goes to one, control transfers to module two.

 

S3 - QIOA1

Block address of the I/O quality for module one. Specifications S3 and S4 define the blocks containing the boolean or real I/O for module one. If the quality of <S3> or <S4> goes bad, control will be transferred to module two, providing it is good quality. If both modules are bad quality, the output is the value from module one, but output N+1 equals logic 1 (both modules are bad). Figure 98-1 shows how to transfer an active I/O module if an analog output goes bad.

 

S4 - QIOB1

Block address of the I/O quality for module one (same as S3).

 

S5 - STTSA2

Block address of the boolean status for module two (refer to S1 description).

 

S6 - STTSB2

Block address of the boolean status for module two (refer to S2 description).

 

S7 - QIOA2

Block address of the quality for module two (refer to S3 description).

 

 

 

S8 - QIOB2

Block address of the quality for module two (refer to S3 description).

 

S9 - TOGGLE

Block address of the toggle input. If both modules are good, a logic 0 to 1 transition of <S9> transfers control to the standby module.

 

 

98.2 Applications

 

Figure 98-2 shows the configuration of a slave select block controlling the redundant analog input (function code 96). The analog input selected depends on the module selected in the slave select. This configuration also shows the interlock (N+1) forcing the output value to a predetermined safe value in the event that both modules are bad.