High-Level Data Link Control (HDLC)
Am186™CC/CH/CU Microcontrollers User’s Manual
15-9
The receive status indicates the following information:
■
If there was an overflow of the receive FIFO
■
If a non-integer number of bytes were received
■
If a CRC error was detected
■
Which address was matched
■
If the frame was too short or too long
■
If the receiver was turned off during the frame
■
If the frame ended with an abort (one zero followed by seven to 14 consecutive 1s).
At the end of frame 1, software must read the status of frame 1 from the receive FIFO before
it can read any data from frame 2.
15.5.3
General HDLC Options
These options involve both the transmitter and the receiver. For transmitter-specific options,
see “HDLC Transmitter” on page 15-10; for receiver-specific options, see “HDLC Receiver”
on page 15-14.
■
Data Clocks: Each HDLC channel requires two clock sources: a transmit clock for the
transmit data, and a receive clock for the receive data.
■
HDLC Reset: To initiate HDLC reset, set the HRESET bit in the HxCON register to 1.
HDLC reset clears the HDLC channels and FIFOs and restores all status registers to
their default values. HDLC reset does not affect the user-programmed control bits.
■
NRZ/NRZI Data Encoding: The microcontroller supports both non-return to zero (NRZ)
and non-return to zero, invert on zero (NRZI) data formats. Specify the encoding format
with the NRZI bit of the HxCON register.
■
Transparent Mode: Transparent mode disables zero-bit insertion and deletion, CRC
generation and checking, abort generation, and opening/closing flag generation. The
HDLC controller transmits data exactly as it is loaded in the transmit FIFO. When the
FIFO is empty, the controller generates idles (mark or flag) and does not set the abort
bit. If CTS is deasserted in Transparent mode, the transmitter goes to the idle state.
Transparent mode also disables the receive byte counter; therefore, short frame and
long frame errors are not reported. Byte alignment is possible in all modes except raw
DCE. Additionally, alignment is not possible when the entire time-multiplexed bus is
allocated to a single TSA/HDLC channel. To enable Transparent mode, set the TRANSM
bit in the HxCON register to 1.
To use byte alignment when using Transparent mode with a time-multiplexed data format,
set, then clear, the HRESET bit in the HxCON register after configuring the TSA and
HDLC channels and establishing operation. The first byte received or transmitted may
be corrupted while the HDLC channel is performing the alignment. To mask this effect
on the transmit side, configure the transmitter to use mark idles and make the first
transmitted byte all 1s (FFh).
To maintain byte alignment, all time slot widths used must be a multiple of eight bits and
there must be at least one empty time slot. HDLC requires the unused time slot to properly
locate the byte boundary. If the transmit FIFO underflows, the transmitter loses byte
alignment.
Содержание Am186 CC
Страница 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Страница 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Страница 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Страница 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Страница 39: ...Architectural Overview Am186 CC CH CU Microcontrollers User s Manual 1 15 Figure 1 6 32 Channel Linecard CH CC...
Страница 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Страница 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Страница 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Страница 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Страница 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...