Rockwell Automation 1770-HT8 SMART TRANSMITTER - Manual (Page 72)

Chapter 4
C Communicating with the Smart
Transmitter Interface
4-7
Short Frame Address Field
This one-byte field contains three bit fields: the master address bit, the
logical address bits and the slave address bits. The master address bit
differentiates between packets sent from a primary or secondary master.
Set this bit to 0 so the Smart Transmitter Interface operates in the preferred
mode of primary master. For those applications requiring a secondary
master set this bit to 1. Since master mode changes at the Smart
Transmitter Interface are dynamic for each message, you can change this
bit for successive messages.
Important: A link to a HART field device can have only one primary and
one secondary master.
Two logical address bits define the addresses of up to four logical devices
within one HART field device. You should clear these bits for most field
devices.
The slave address bits range from decimal 0 to 15. Most applications with
point-to-point HART links require a slave address of 0. However, HART
field devices only recognize polling addresses of 1 to 15 when placed into
multi-drop mode and assigned a polling address using HART Command
#6.
When the field device is on a point-to-point link, set this field to
hexadecimal 80 for a primary master or hexadecimal 00 for a secondary
master. On a multi-drop link, set this field to a value in the range
hexadecimal 80 to hexadecimal 8F for a primary master and hexadecimal
00 to hexadecimal 0F for a secondary master.
Long Frame Address Field
This five-byte field contains two bit fields: the master address bit, and a 38
bit device address. The master address bit is defined as for short frame
address fields. Figure 4.5 illustrates the format of the 38 bit device address.
Use HART Command #0 and short frame addressing (as illustrated in the
programmable controller programming example later in this chapter) to
determine this address.