Serial Communications Overview
Am186™CC/CH/CU Microcontrollers User’s Manual
12-7
Figure 12-5
CTS/RTR Protocol
12.3.3
FIFOs
Another way to reduce data overflow is to use a hardware
FIFO (First In First Out data
buffer). A hardware FIFO queues up the bytes until the receiver is ready for them. A FIFO
is classified by its width and depth. The width specifies the number of bits in a word; the
depth, the number of those words that can be queued. So, a 9x16 FIFO can queue 16 9-bit
words before overflowing. FIFOs can also be useful when data arrives during an interrupt.
In the Am186CC microcontroller, FIFOs are available for the High-Speed UART, HDLC,
and USB ports.
In the Am186CH HDLC microcontroller, FIFOs are available for the High-Speed UART and
HDLC ports.
In the Am186CU USB microcontroller, FIFOs are available for the High-Speed UART and
USB ports.
12.3.4
Polled, Interrupt, and DMA Modes
Serial communications can occur in polled, interrupt, or DMA modes.
Polled mode disables
interrupts and the DMA controller. The software loops on a status register, reading in all
wait situations. In
interrupt mode, interrupts are enabled. Software does other tasks while
waiting for the interrupt. In
DMA mode, hardware performs the entire transfer, with no
software intervention except for errors. For information about interrupts, see Chapter 7,
“Interrupts.” For information about DMA, see Chapter 8, “DMA Controller.”
In the Am186CC/CH/CU microcontrollers, the serial communications peripherals support
the three modes as follows:
■
The UART and High-Speed UART support polled, interrupt, and DMA modes.
■
The SSI only supports polled mode.
■
In the Am186CC and Am186CH microcontrollers, the HDLC channels support polled,
interrupt, and DMA modes.
■
In the Am186CC microcontroller, GCI supports polled and interrupt modes but not DMA
mode.
■
In the Am186CC and Am186CU microcontrollers, USB supports polled, interrupt, and
DMA modes.
Transmitter
CTS
RTR
CTS
RTR
CTS = Input signal to the transmitter; clear to send input
Port 1
Port 2
Transmitter
Receiver
Receiver
RTR = Output signal from the receiver; ready to receive output
CC
CH
CU
CH
CC
CC
CU
CC
Summary of Contents for Am186 CC
Page 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Page 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Page 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Page 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Page 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Page 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Page 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Page 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Page 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...