Status Byte Register; Service Request Enable Register; Reading Registers; Programming Registers - Lakeshore 335 User Manual

94 c 6: Computer Interface Operation
HAPTER
Model 335 Temperature Controller

6.2.4.4 Status Byte Register

The Status Byte register, typically referred to as the Status Byte, is a non-latching,
read-only register that contains all of the summary bits from the register sets. The
status of the summary bits are controlled from the register sets as explained in sec-
tion 6.2.4.1 to section 6.2.4.3. The Status Byte also contains the Request for Service
(RQS)/Master Summary Status (MSS) bit. This bit is used to control the Service
Request hardware line on the bus and to report if any of the summary bits are set via
the *STB? command. The status of the RQS/MSS bit is controlled by the summary bits
and the Service Request Enable Register.

6.2.4.5 Service Request Enable Register

The Service Request Enable Register determines which summary bits in the Status
Byte will set the RQS/MSS bit of the Status Byte. The user may write to or read from
the Service Request Enable Register. Each Status Byte summary bit is logically ANDed
to the corresponding enable bit of the Service Request Enable Register. When a Ser-
vice Request Enable Register bit is set by the user, and the corresponding summary bit
is set in the Status Byte, the RQS/MSS bit of the Status Byte will be set, which in turn
sets the Service Request hardware line on the bus.

6.2.4.6 Reading Registers

Any register in the status system may be read using the appropriate query command.
Some registers clear when read, others do not (section 6.2.4.8). The response to a
query will be a decimal value that corresponds to the binary-weighted sum of all bits
in the register (TABLE 6-2). The actual query commands are described later through-
out section 6.4.1.
Position B7
Decimal 128
Weighting 2 7
Example: If bits 0, 2, and 4 are set, a query of the register will return a decimal value of 21 (1+4+16).
TABLE 6-2 Binary weighting of an 8-bit register

6.2.4.7 Programming Registers

The only registers that may be programmed by the user are the enable registers. All
other registers in the status system are read-only registers. To program an enable
register, send a decimal value that corresponds to the desired binary-weighted sum
of all bits in the register (TABLE 6-2). The actual commands are described throughout
(section 6.4.1).
B6 B5 B4
64 32 16
2 6 2 5 2 4
B3 B2 B1
8 4 2
2 3 2 2 2 1
B0
1
2 0