Motorola DragonBall MC68328 User Manual page 105

UART
TXD Transmit Data
This pin is the transmitter serial output. While in normal mode, NRZ data is output. While
in IrDA mode, a 3/16 bit-period pulse is output for each 0 bit transmitted. For RS-232 ap-
plications, this pin must be connected to an RS-232 transmitter. For infrared applications,
this pin can directly drive an infrared tranceiver module.
Clear To Send
CTS
This active-low input controls the transmitter. Normally, the transmitter waits until this sig-
nal is active (low) before transmitting a character. If the IGNORE CTS bit is set, the trans-
mitter sends a character whenever a character is ready to transmit. This signal can then
serve as a general-purpose input with a read status in the CTS STATUS bit. This pin can
post an interrupt on any transition of itself if the interrupt is enabled.
RXD Receive Data
This pin is the receiver serial input. While in normal operation, NRZ data is expected.
While in IrDA mode, a narrow pulse is expected for each 0 bit received. Use external cir-
cuitry to convert the infrared signal to an electrical signal. RS-232 applications need an
external RS-232 receiver to convert from RS-232 voltage levels.
RTS Ready To Send
This output pin serves two purposes. Normally, the receiver indicates that it is ready to
receive data by asserting this pin (low). This pin would be connected to the far-end trans-
mitter's CTS pin. When the receiver detects a pending overrun, it negates this pin. For oth-
er applications, this pin can serve as a general-purpose output controlled by the RTS bit
in the receiver register.
GPIO General-Purpose Input/Output
This bidirectional pin serves several functions. It can be a general-purpose input that: (1)
can post interrupts on any transition, (2) is controlled by the GPIO bit in the baud register,
8-2 MC68328 DRAGONBALL PROCESSOR USER'S MANUAL
RX
RECEIVER
FIFO
TX
TRANSMITTER
FIFO
BAUD GEN
Figure 8-1. UART Block Diagram
RXD
TXD
GPIO
CTS
RTS
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