Function Code 01H/02H: Read Binary Status - GE 750 Instruction Manual

16.3 MODBUS PROTOCOL
These function codes allow the master to read one or more consecutive binary status bits from an 750/760.
The status bits are packed into bytes with the first addressed bit occupying the least significant bit position of
the first returned byte. Enough bytes are returned to contain all requested status bits. The last byte is zero-pad-
ded as required. The maximum number of status bits that can be read in a single request is 1920 (although this
greatly exceeds the number of status bits defined in the 750/760).
The addresses of the bits that can be read using these functions are the same as the point indices defined for
the DNP Binary Input objects (e.g., address zero references the "Relay In Service" status). Refer to Section
16.5: DNP 3.0 DEVICE PROFILE on page 16–84 for the definition of all binary status data. Note that function
codes 01H and 02H are identical in their operation.
The following table shows the format of the master and slave packets. The example shows a master device
requesting 10 status bit values starting at address 13h from slave device 11; the slave device responds with
the bit values 1, 0, 1, 1, 0, 0, 1, 0, 0 and 1 from binary status addresses 13h through 1Ch inclusive. Note that
two bytes are required to contain the response data. The first byte contains the first eight data bits stored in the
least significant to the most significant bit position. The second byte contains the last two data bits stored in the
least two significant bit positions. Note that the rest of the second byte is zero-filled.
Table 16–2: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 01H/02H
MASTER TRANSMISSION
PACKET FORMAT
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS - hi
DATA STARTING ADDRESS - lo
16
NUMBER OF DATA BITS - hi
NUMBER OF DATA BITS - lo
CRC - lo
CRC - hi
16-
6
Courtesy of NationalSwitchgear.com

16.3.5 FUNCTION CODE 01H/02H: READ BINARY STATUS

EXAMPLE (HEX)
11
01
00
13
00
0A
4F
58
750/760 Feeder Management Relay
16 COMMUNICATIONS
SLAVE RESPONSE
PACKET FORMAT
SLAVE ADDRESS
FUNCTION CODE
BYTE COUNT
DATA BYTE #1 - hi
DATA BYTE #2 - lo
CRC - lo
CRC - hi
GE Power Management
EXAMPLE (HEX)
11
01
02
4D
02
CC
AE