
Asynchronous Serial Port
10-2
Table 10-1
Serial Port External Pins
Each port is provided with two data pins (RXD0/RXD1 and TXD0/TXD1) and two flow control
signals (RTS0, RTS1/RTR0, RTR1). The flow control signals are configurable by software
to support several different protocols. These protocols are discussed below. Hardware flow
control is enabled for the serial port when the FC bit in the serial port control register is set.
10.1.1.1
DCE/DTE Protocol
The Am186ES and Am188ES microcontrollers implement only a subset of the data
communication equipment/data terminal equipment (DCE/DTE) protocol. The DCE/DTE
protocol provides flow control where one serial port is receiving data and the other serial
port is sending data, as shown in 10.1.1.2.
Figure 10-1
DCE/DTE Protocol
10.1.1.2
DCE/DTE Protocol
The Am186ES and Am188ES microcontrollers’ serial ports can function as either DTE or
DCE devices. To implement the DCE device, the ENRX bit should be set and the RTS bit
should be cleared for the associated serial port. To implement the DTE device, the ENRX
bit should be cleared and the RTS bit should be set for the associated serial port. These
bits are located in the AUXCON register.
In the DCE/DTE protocol, the DTE device sends data. When data is available to send, the
DTE device asserts the RTS signal. The RTS signal is interpreted by the DCE device as a
request to enable its receiver. The DCE device signals the DTE device that it is ready to
receive data by asserting the RTR signal. The interface is asymmetrical since the DTE
device cannot signal the DCE device that it is ready to receive data; neither can the DCE
device signal that it is ready to send data.
Pin
Designation
Pin Function
RXD0, RXD1
Receives serial port data
TXD0, TXD1
Transmits serial port data
CTS0, CTS1/
ENRX0, ENRX1
Clear to send or enable receiver
request
RTS0, RTS1/
RTR0, RTR1
Ready to send or ready to receive
DCE
DTE
ENRX
RTR
CTS
RTS
RTS = Request to send output from transmitter
CTS = Clear to send input to transmitter
RTR = Ready to receive output from receiver
ENRX = Enable receiver request input to receiver
Summary of Contents for Am186 ES
Page 1: ...Am186 ES and Am188 ES User s Manual...
Page 4: ...iv...
Page 12: ...Table of Contents xii...
Page 22: ...Features and Performance 1 8...
Page 60: ...System Overview 3 28...
Page 84: ...Chip Select Unit 5 14...
Page 132: ...Timer Control Unit 8 8...
Page 166: ...Programmable I O Pins 11 6...
Page 184: ...Register Summary A 18...