Motorola MPC8260 PowerQUICC II User Manual page 626

Part IV. Communications Processor Module
Figure 21-10 shows the most common HDLC bus LAN conÞguration, a multimaster
conÞguration. A station can transfer data to or from any other LAN station. Transmissions
are half-duplex, which is typical in LANs.
RXD TXD
HDLC Bus
Controller
A
RCLK/TCLK
Clock
Master
NOTES
:
1. Transceivers may be used to extend the LAN size.
2. The TXD pins of slave devices should be configured to open-drain in the port C parallel I/O port.
3. Clock is a common RCLK/TCLK for all stations.
Figure 21-10. Typical HDLC Bus Multimaster Configuration
In single-master conÞguration, a master station transmits to any slave station without
collisions. Slaves communicate only with the master, but can experience collisions in their
access over the bus. In this conÞguration, a slave that communicates with another slave
must Þrst transmit its data to the master, where the data is buffered in RAM and then resent
to the other slave. The beneÞt of this conÞguration, however, is that full-duplex operation
can be obtained. In a point-to-multipoint environment, this is the preferred conÞguration.
Figure 21-11 shows the single-master conÞguration.
21-18
HDLC Bus LAN
CTS RXD TXD
HDLC Bus
Controller
B
RCLK/TCLK
Master
MPC8260 PowerQUICC II UserÕs Manual
CTS RXD TXD
HDLC Bus
Controller
C
RCLK/TCLK
Master
+ 5 V
R
CTS
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