High-Level Data Link Control (HDLC)
Am186™CC/CH/CU Microcontrollers User’s Manual
15-15
Note: The HDLC receiver requires frames two bytes or longer. The HDLC transmitter
requires at least one byte of data surrounded by flags: the start flag, one byte of data, and
the end flag. A 2-byte CRC with no data also constitutes a valid transmission.
Figure 15-7
HDLC Receiver Block Diagram
The HDLC receivers have the following features:
■
Flag/Abort Detection: A flag must be detected before starting to receive a frame. A
frame ends and status is reported when the receiver detects a flag or abort sequence.
The Am186CC and Am186CH microcontrollers support receiving back-to-back frames
with only one flag between frames. In Transparent mode, flag/abort delineation is
disabled, and reception begins as soon as the receiver is enabled. Reception continues
until the receive FIFO overflows.
■
Zero-Bit Deletion: Between the opening and closing flags, the receiver removes any 0
that appears after a string of five consecutive 1s (these 0s are added during transmission
to prevent a data pattern from resembling an abort, or an opening or closing flag).
■
Receive-Byte Counter: The receive-byte counter counts the number of bytes received
between flags. If the number is less than a 4-bit programmable number, the frame has
an error status reported, and part of the frame may be truncated. The receiver rejects
very short frames (less than two bytes) and does not put them into the receive FIFO.
Short frames (less than the value set in the MINRL field of the HxRCON0 register) and
very short frames each generate a separate maskable interrupt. Frames that are
truncated due to an abort condition do not count as short or very short frames. If the
number of bytes received exceeds a 16-bit programmable number, current frame
reception stops, an error status is reported, and the receiver begins to look for a flag.
Transparent mode operation disables the receive-byte counter.
■
Receive-Clock Polarity: The receive-clock polarity is programmable through the
RXCINV bit in the HxTCON0 register, independent of the transmit clock polarity. An
inverted clock is recommended for use only in DCE mode.
■
Frame Status: At the end of reception, the receiver places the receive byte counter
value and one byte of frame status in the receive FIFO. In programmed I/O mode, the
frame status becoming available generates a maskable interrupt, indicated in the REOF
bit of the HxISTAT0 register.
En
d-o
f-Fram
e
Serial
CRC Checker (16- or 32-bit)
Zero
Del.
Flag/Abort
Detection
Address
Detector
Shift Register
Shift Register
FIFO
Short Frame Det.
Transparent Mode Path
DMA & Threshold
Logic
DRQ
Byte Clock
Byte Counter
Long Frame Det.
Input
Ta
g
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...