AM186ES Advanced Micro Devices, AM186ES Datasheet - Page 149

• Manufacturer Part Number: AM186ES
• Description: microcontrollers provide a low-cost/ high-performance solution for embedded system designers who wish to use the x86 architecture.
• Manufacturer: Advanced Micro Devices

10.1.1.3
Figure 10-2
10.1.1.4
10.2
CTS/RTR Protocol
Note: The clear-to-send/ready-to-receive (CTS/RTR) protocol provides flow control when
both ports are sending and receiving data, as shown in Figure 10-2.
CTS/RTR Protocol
The Am186ES and Am188ES microcontrollers’ serial ports can be configured for the CTS/
RTR protocol by clearing both the ENRX and the RTS bits for the associated serial port.
This is the default configuration.
The CTS/RTR protocol provides a symmetrical interface. When a device is ready to receive
data, i.e., there is no unread data in the serial port receive register, the device asserts the
RTR signal. A device does not begin transmitting data until the CTS signal is asserted.
Flow Control and Transmission Rates
Although the use of flow control can eliminate the possibility of overrun errors—data loss
due to reception of new data before the last received data has been read—it can have an
effect on serial port transmission rates.
On the Am186ES and Am188ES microcontrollers, the RTR signal is not asserted until valid
data from a previous transmission has been read out of the receive register, i.e., the RDR
bit in the serial port status register is cleared. This means that the transmitting serial port
will not begin transmission of the next data item until software running on the Am186ES
and Am188ES microcontrollers has had a chance to read the last data item. This is not the
case when flow control is not being used and data continues to be sent, allowing software
a minimum of one frame transmission time to read the data in order to prevent overrun
errors. To minimize this delay, the receive register should be read as soon as possible after
the completion of the reception of data. Using the serial port receiver as a DMA source
provides the shortest possible delay.
PROGRAMMABLE REGISTERS
The asynchronous serial ports are programmed through the use of 10, 16-bit peripheral
registers. See Table 10-2.
CTS = Clear to send input to transmitter
RTR = Ready to receive output from receiver
RTR
CTS
Asynchronous Serial Port
RTR
CTS
10-3