Motorola MPC8260 User Manual

29-85

MOTOROLA

The UTOPIA interface supports loop-back mode. In this mode, the Rx and Tx UTOPIA
signals are shorted internally. Output pins are driven; input pins are ignored. 

Note that in loop-back mode, the transmitter and receiver must operate in complementary
modes. For example, if the transmitter is master, the receiver must be a slave
(FPSMR[TUMS] = 0, FPSMR[RUMS] = 1).

Modes are selected through GFMR[DIAG], as shown in Table 29-46. 

The following sections describe the conÞguration of the registers in ATM mode.

The GFMR mode Þeld should be programmed for ATM mode. To enable transmit and
receive functions, ENT and ENR must be set as the last step in the initialization process.
Full GFMR details are given in Section 28.2, ÒGeneral FCC Mode Registers (GFMRx).Ó 

The FCC protocol-speciÞc mode register (FPSMR), shown in Figure 29-59, controls
various protocol-speciÞc FCC functions. The user should initialize the FPSMR. Erratic
behavior may result if there is an attempt to write to the FPSMR while the transmitter and
receiver are enabled.

00

Normal mode

01

Loop-back. UTOPIA Rx and Tx signals are shorted internally. Output pins are driven, input pins are ignored.

1x

Reserved