User`s guide

32 DC 900-1317J
ADCCP NRM Programmer’s Guide
In an unbalanced configuration (see Figure 2–1), the primary station transmits com-
mands and the secondary stations transmit responses. Two modes of operation are
defined in an unbalanced configuration: normal response mode and asynchronous
response mode.
In normal response mode, secondary stations are forbidden to transmit information
frames until invited to do so by the primary station. This invitation to transmit occurs
when the primary station sends any frame with the P-bit (poll bit) set. The secondary
station’s response ends when it transmits a frame with the F-bit (final bit) set.
In asynchronous response mode, the secondary stations may send unsolicited informa-
tion frames at any time. These information frames contain an F-bit that is reset to zero.
However, when a secondary station receives (from the primary station) a command
frame that has the P-bit set to one, the secondary station must respond as soon as pos-
sible with a frame that has the F-bit set to one. If multiple secondary stations are config-
ured for ARM operation, special hardware is required to prevent contention on the
link.
Figure 2–1: Unbalanced Configuration
Primary
Station
on link
Secondary
Station
A
Secondary
Station
B
(optional)
Secondary
Station
C
(optional)
Commands
Responses
DRWG-0526