MC68340 datasheet(325/441 Pages) FREESCALE

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7- 30

MC68340 USER’S MANUAL

MOTOROLA

RC1–RC0—Receiver Commands

These bits select a single command as listed in Table 7-8.

Table 7-8. RCx Control Bits

RC1

RC0

Command

No Action Taken

Enable Receiver

Disable Receiver

Do Not Use

No Action Taken—The no action taken command causes the receiver to stay in its

current mode. If the receiver is enabled, it remains enabled; if disabled, it remains

disabled.

Receiver Enable—The receiver enable command enables operation of the channel's

receiver. If the serial module is not in multidrop mode, this command also forces the

receiver into the search-for-start-bit state. If the receiver is already enabled, this

command has no effect.

Receiver Disable—The receiver disable command disables the receiver immediately.

Any character being received is lost. The command has no effect on the receiver status

bits or any other control register. If the serial module is programmed to operate in the

local loopback mode or multidrop mode, the receiver operates even though this

command is selected. If the receiver is already disabled, this command has no effect.

Do Not Use—Do not use this bit combination because the result is indeterminate.

7.4.1.8 RECEIVER BUFFER (RB). The receiver buffer contains three receiver holding

registers and a serial shift register. The channel's RxDx pin is connected to the serial shift

while the receiver shifts and updates from the bottom of the stack when the shift register

has been filled (see Figure 7-4). This register can only be read when the serial module is

enabled (i.e., the STP bit in the MCR is cleared).

RBA, RBB

$713, $71B

76543210

RB7

RB6

RB5

RB4

RB3

RB2

RB1

RB0

RESET:

00000000

Read Only

Supervisor/User

RB7–RB0—These bits contain the character in the receiver buffer.

7.4.1.9 TRANSMITTER BUFFER (TB). The transmitter buffer consists of two registers,

the transmitter holding register and the transmitter shift register (see Figure 7-4). The

holding register accepts characters from the bus master if the TxRDY bit in the channel's

SR is set. A write to the transmitter buffer clears the TxRDY bit, inhibiting any more

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