MPC8280 datasheet(688/1386 Pages) FREESCALE

688 / 1386 page

Serial Communications Controllers (SCCs)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

20-8

Freescale Semiconductor

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 Section 20.3.5, “Controlling SCC Timing with RTS, CTS,

and 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 SI

xMR[SDMx]; see Section 15.5.2, “SI Mode

Registers (SIxMR).”

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 20.3.7,

“Reconfiguring the SCCs,” 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.

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 20.3.7,

“Reconfiguring the SCCs,” 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 flow control option in UART mode, and the R bit of the TxBD, also provide the capability to

control the transmitter.

Table 20-2. GSMR_L Field Descriptions (continued)

Bit

Name

Description

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