
CD2481 —
Programmable Four-Channel Communications Controller
4
Datasheet
5.4
DMA Operation ...................................................................................................45
5.4.1
Bus Acquisition Cycle.............................................................................46
5.4.2
DMA Data Transfer ................................................................................46
5.4.3
Bus Error Handling.................................................................................47
5.4.4
A and B Buffers and Chaining................................................................48
5.4.5
Transmit DMA Transfer..........................................................................49
5.4.6
Synchronous Transmitter Examples ......................................................50
5.4.7
Receive DMA Transfer...........................................................................52
Bit Rate Generation and Data Encoding.............................................................60
Hardware Configurations ....................................................................................67
5.6.1
Interface to a 32-Bit Data Bus................................................................68
5.6.2
DMA Connections for the CD2481.........................................................68
5.6.3
Recommended CD2481 as a DTE and DCE Interface..........................68
Microcode Download
..............................................................................................70
6.1
Microcode Download Information........................................................................70
6.1.1
Registers Specific to Download Operations...........................................70
6.1.2
Download Code Example.......................................................................71
Protocol Processing
...............................................................................................75
7.1
HDLC Processing................................................................................................75
7.1.1
FCS (Frame Check Sequence)..............................................................75
7.1.2
HDLC Transmit Mode.............................................................................75
7.1.3
HDLC Receive Mode .............................................................................76
7.2
PPP (Point-to-Point Protocol) Mode....................................................................77
7.2.1
Character Format...................................................................................77
7.2.2
Frame Format ........................................................................................77
7.2.3
FCS (Frame Check Sequence)..............................................................77
7.2.4
Transparency .........................................................................................78
7.2.5
Definition of a Valid Frame.....................................................................79
7.2.6
Transmitter.............................................................................................79
7.2.7
Receiver.................................................................................................80
7.3
SLIP Processing..................................................................................................81
7.3.1
Framing..................................................................................................81
7.3.2
Debugging Aids......................................................................................82
7.4
MNP4
/ARAP Protocol Processing......................................................................82
7.4.1
Framing..................................................................................................82
7.4.2
MNP4
/ARAP FCS (Frame Check Sequence) Calculation.....................83
7.5
Async Processing................................................................................................83
7.5.1
Transmitter In-Band Flow Control ..........................................................83
7.5.2
Receiver In-Band Flow Control ..............................................................84
7.5.3
Out-of-Band Flow Control ......................................................................85
7.5.4
Line Break Detection and Generation....................................................86
7.5.5
Special Character Transmission ............................................................86
7.5.6
Special Character Recognition...............................................................87
7.5.7
Special Character Range.......................................................................87
7.5.8
UNIX Support Features..........................................................................88
7.6
Bisync Protocol ...................................................................................................92
7.6.1
Bisync Transmit Processing...................................................................92
7.6.2
Bisync Receive Processing....................................................................92
5.5
5.6
6.0
7.0