Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 655

Bits Name
24–25 DIAG Diagnostic mode.
00 Normal operation, CTS and CD are under automatic control. Data is received through RXD and
transmitted through TXD. The SCC uses modem signals to enable or disable transmission and
reception. These timings are shown in
CD."
01 Local loopback mode. Transmitter output is connected internally to the receiver input, while the
receiver and the transmitter operate normally. The value on RXD is ignored. If enabled, data appears
on TXD, or the parallel I/O registers can be programmed to make TXD high. RTS can also be
programmed to be disabled in the appropriate parallel I/O register. The transmitter and receiver must
share the same clock source, but separate CLK x 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 SCC by configuring the
associated CTS and CD pins as general-purpose I/O.
10 Automatic echo mode. The transmitter automatically resends received data bit-by-bit using the Rx
clock provided. The receiver operates normally and receives data if CD is asserted. CTS is ignored.
11 Loopback and echo mode. Loopback and echo operation occur simultaneously. CD and CTS are
ignored. See the loopback bit description above for clocking requirements.
For TDM operation, the diagnostic mode is selected by SIMODE[SDM x ]; see
Register (SIMODE)."
26 ENR Enable receive. Enables the receiver hardware state machine for the SCC.
0 The receiver is disabled and data in the Rx FIFO is lost. If ENR is cleared during reception, the
receiver aborts the current character.
1 The receiver is enabled.
ENR can be set or cleared, regardless of whether serial clocks are present.
"Reconfiguring the SCCs,"
provided for controlling SCC reception: the
27 ENT Enable transmit. Enables the transmitter hardware state machine for the SCC.
0 The transmitter is disabled. If ENT is cleared during transmission, the current character is aborted and
TXD returns to the idle state. Data already in the Tx shift register is not sent.
1 The transmitter is enabled.
ENT can be set or cleared, regardless of whether serial clocks are present.
"Reconfiguring the SCCs,"
provided for controlling SCC transmission: the
TRANSMIT
28–31 MODE Channel protocol mode. See also GSMR_H[TTX, TRX].
0000 HDLC
0001 Reserved
0010 AppleTalk/LocalTalk
0011 SS7—reserved for RAM microcode
0100 UART
0101 Reserved
0110 Asynchronous HDLC or IrDA
0111 Reserved.
1000 BISYNC
1001 Reserved
101x Reserved
1100 Ethernet
All others reserved
Freescale Semiconductor
Table 21-3. GSMR_L Field Descriptions (continued)
describes how to disable/enable the SCCs. Note also these other tools
describes how to disable/enable the SCCs. Note also these other tools
commands, the freeze option and CTS flow control option in UART mode, and TxBD[R].
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Description
Section 21.4.4, "Controlling SCC Timing with RTS, CTS, and
and
ENTER HUNT MODE CLOSE RXBD
,
STOP TRANSMIT GRACEFUL STOP TRANSMIT
Serial Communications Controllers
Section 20.2.4.2, "SI Mode
Section 21.4.7,
commands, and RxBD[E].
Section 21.4.7,
, and
RESTART
21-9