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MC68349 USER'S MANUAL
MOTOROLA
2.13.3 DMA Done (
DONE2, DONE1 )
This active-low bidirectional signal is asserted by the DMA or a peripheral device during
any DMA bus cycle to indicate that the last data transfer is being performed. DONE≈ is an
active input in any mode. As an output, it is only active in external request mode. An
external pullup resistor is required even during operation in the internal request mode.
2.14 SERIAL MODULE SIGNALS
The following signals are used by the serial module for data and clock signals. See
Section 8 Serial Module for more information on these signals.
2.14.1 Serial External Clock Input (SCLK)
This input can be used as the external clock input for channel A or channel B, bypassing
the baud rate generator.
2.14.2 Serial Crystal Oscillator (X1, X2)
These pins furnish the connection to a crystal or external clock, which must be supplied
when using the baud rate generator. An external clock should be connected to the X1 pin
with X2 left floating.
2.14.3 Receive Data (RxDA, RxDB)
These signals are the receiver serial data input for each channel. Data received on this
signal is sampled on the rising edge of the clock source, with the least significant bit
received first.
2.14.4 Transmit Data (TxDA, TxDB)
These signals are the transmitter serial data output for each channel. The output is held
high ('mark' condition) when the transmitter is disabled, idle, or operating in the local
loopback mode. Data is shifted out on this signal at the falling edge of the clock source,
with the least significant bit transmitted first.
2.14.5 Receiver Ready (
RRDYA)
This active-low output signal can be programmed as the channel A receiver ready,
channel A first-in-first-out (FIFO) full indicator, or a dedicated parallel output.
RRDYA
When used for this function, this signal reflects the complement of the status of bit 1 of
the serial interrupt status register. This signal can be used to control parallel data flow
by acting as an interrupt to indicate when the receiver contains a character.