Motorola PowerQUICC II MPC8280 Series Reference Manual page 994

General FCC Mode Registers (GFMRx)
0 1 2
Field DIAG TCI
Reset
R/W
Addr
16 17 18
Field SYNL RTSM
Reset
R/W
Addr
Figure 30-2. General FCC Mode Register (GFMR)
Table 30-2. describes GFMR fields.
Table 30-2. GFMR Register Field Descriptions
Bits Name
0–1 DIAG Diagnostic mode.
00 Normal operation—Receive data enters through RXD, and transmit data is shifted out through
TXD. The FCC uses the modem signals (CD and CTS) to automatically enable and disable
transmission and reception. Timings are shown in Section 30.11, "FCC Timing Control."
01 Local loopback mode—Transmitter output is connected internally to the receiver input, while the
receiver and the transmitter operate normally. RXD is ignored. Data can be programmed to
appear on TXD, or TXD can remain high by programming the appropriate parallel port register.
RTS can be disabled in the appropriate parallel I/O register. The transmitter and receiver must
use the same clock source, but separate CLKx pins can be used if connected to the same
external clock source.
If external loopback is preferred, program DIAG for normal operation and externally connect TXD
and RXD. Then, physically connect the control signals (RTS connected to CD, and CTS
grounded) or set the parallel I/O registers so CD and CTS are permanently asserted to the FCC
by configuring the associated CTS and CD pins as general-purpose I/O.; see Chapter 41,
"Parallel I/O Ports."
10 Automatic echo mode—The channel automatically retransmits received data, using the receive
clock provided. The receiver operates normally and receives data if CD is asserted. The
transmitter simply transmits received data. In this mode, CTS is ignored. The echo function can
also be accomplished in software by receiving buffers from an FCC, linking them to TxBDs, and
transmitting them back out of that FCC.
11 Loopback and echo mode—Loopback and echo operation occur simultaneously. CD and CTS
are ignored. Refer to the loopback bit description for clocking requirements.
For TDM operation, the diagnostic mode is selected by SIxMR[SDMx]; see Section 15.5.2, "SI Mode
Registers (SIxMR)."
2 TCI Transmit clock invert
0 Normal operation.
1 The FCC inverts the internal transmit clock.
The edge on which the FCC outputs the data depends on the protocol:
• In HDLC and Transparent mode, when TCI=0, data is sent on the falling edge; when TCI=1, on
the rising edge.
• In Ethernet mode, when TCI=0, data is sent on the rising edge; when TCI=1, on the falling edge.
30-4
Freescale Semiconductor, Inc.
3 4 5 6
TRX TTX CDP CTSP CDS CTSS
0000_0000_0000_0000
0x11300 (GFMR1), 0x11320(GFMR2), 0x11340(GFMR3)
19 20 21 22
RENC REVD TENC
0000_0000_0000_0000
0x11302 (GFMR1), 0x11322 (GFMR2), 0x11342 (GFMR3)
MPC8280 PowerQUICC II Family Reference Manual
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7 8 9 10 11
R/W
23 24 25 26 27
TCRC ENR ENT
R/W
Description
12 13 14 15
—
28 29 30 31
MODE
MOTOROLA