Motorola MPC8260 - Manual (Page 630)

21-22 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part IV. Communications Processor Module
Figure 21-15. Delayed RTS Mode
21.14.5 Using the Time-Slot Assigner (TSA)
HDLC bus controllers can be used with a time-division multiplexed transmission line and
a local bus, as shown in Figure 21-16. Local stations use time slots to communicate over
the TDM transmission line; stations that share a time slot use the HDLC bus protocol to
control access to the local bus.
Figure 21-16. HDLC Bus TDM Transmission Line Configuration
The local SCCs in HDLC bus mode communicate only with the transmission line and not
with each other. The SCCs use the TSA of the serial interface, receiving and sending data
over L1TXDx and L1RXDx. Because collisions are still detected from the individual SCC
CTS pin, it must be conÞgured to connect to the chosen SCC. Because the SCC only
receives clocks during its time slot, CTS is sampled only during the Tx clock edges of the
particular SCC time slot.
TCLK
RTS active for
only 2 bit times
TXD
CTS
RTS
1st Bit 2nd Bit 3rd Bit
Collision
Local HDLC Bus
HDLC Bus
Controller
L1RXD CTS L1TXD
B
HDLC Bus
Controller
L1RXD CTS L1TXD
D
+ 5 V
R
NOTES:
1. All TXD pins of slave devices should be configured to open-drain in the port C parallel I/O port.
2. The TSA in the SI of each station is used to configure the preferred time slot.
Tx
Rx
Line Driver
HDLC Bus
Controller
L1RXD CTS L1TXD
C
HDLC Bus
Controller
L1RXD CTS L1TXD
A
Stations share time-slot n Stations share time-slot m
3. The choice of the number of stations to share a time slot is user-defined. It is two in this example.