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Physical Layer Interface Controller (PLIC)
MCF5272 ColdFire Integrated Microprocessor User’s Manual, Rev. 3
Freescale Semiconductor
13-9
13.2.4.1
Automatic Echo Mode
The port automatically retransmits the received data on a bit-by-bit basis in this mode. The local
CPU-to-receiver communication continues normally, but the CPU-to-transmitter link is disabled. While in
this mode, received data is clocked on the receiver clock and retransmitted on transmit Dout pin.
13.2.4.2
Local Loopback Mode
TxData is internally connected to RxData in this mode. This mode is useful for testing the operation of a
local port by sending data to the transmitter and checking data assembled by the receiver. In this manner,
correct channel operations can be assured. Also, both transmitter and CPU-to-receiver communications
continue normally in this mode. While in this mode, the receive Din pin is ignored, the transmit Dout is
held marking, and the receiver is clocked by the transmitter clock.
13.2.4.3
Remote Loopback Mode
The channel automatically transmits received data on the transmit Dout pin on a bit-by-bit basis in this
mode. The local CPU-to-transmitter link is disabled. This mode is useful in testing receiver and transmitter
operation of a remote channel. While in this mode, the receiver clock is used for the transmitter.
Figure 13-9. GCI/IDL Loopback Mode
13.2.5
GCI/IDL Interrupts
The PLIC module generates two interrupts—the periodic frame interrupt and the aperiodic status interrupt.
13.2.5.1
GCI/IDL Periodic Frame Interrupt
The frame interrupt is a periodic 2-KHz interrupt as shown in
Figure 13-10. This is the normal interrupt
rate for servicing the incoming and outgoing B and D channels. This service routine must execute in a
timely manner. Each of the B- and D-channel transmit and receive registers should be written and read
prior to the next 2-KHz interrupt for underrun or overrun conditions to be prevented.
Disabled
CPU
Rx
Tx
Disabled
(a) Automatic Echo
Disabled
CPU
Rx
Tx
Disabled
(b) Local Loopback
Din
Dout
Din
Dout
CPU
Rx
Tx
(c) Remote Loopback
Din
Dout
Disabled