Motorola MPC8260 用户手册

19-8

MOTOROLA

24Ð25 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 Section 19.3.5, ÒControlling SCC Timing with RTS, CTS, 
and CD.Ó

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 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 SCC by 
conÞguring 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 SIxMR[SDMx]; see Section 14.5.2, ÒSI Mode 
Registers (SIxMR).Ó

26

ENR

Enable receive. Enables the receiver hardware state machine for this 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. Section 19.3.8, 
ÒReconÞguring the SCCs,Ó describes how to disable/enable an SCC. Note that other tools, including 
the

 

ENTER

 

HUNT

 

MODE

 

and 

CLOSE

 

RXBD

 

commands and the E bit of the Rx BD, data provide the 

capability to control the receiver.

27

ENT

Enable transmit. Enables the transmitter hardware state machine for this 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. Section 19.3.8, 
ÒReconÞguring the SCCs,Ó describes how to disable/enable an SCC. Note that other tools, such as 
the 

STOP

 

TRANSMIT

, 

GRACEFUL

 

STOP

 

TRANSMIT

, and 

RESTART

 

TRANSMIT

 commands, the freeze option 

and CTS ßow control option in UART mode, and the R bit of the TxBD, also provide the capability to 
control the transmitter.

28Ð31 MODE Channel protocol mode. See also GSMR_H[TTX, TRX].

0000 HDLC
0001 Reserved
0010 AppleTalk/LocalTalk
0011 SS7Ñreserved for RAM microcode
0100 UART
0101 ProÞbusÑreserved for RAM microcode
0110 Reserved
0111 Reserved
1000 BISYNC
1001 Reserved
101x Reserved
1100 Ethernet 
11xx Reserved