Hardware manual

Table of Contents
Serial HOWTO
16.14 "Device /dev/ttyS? is locked.".....................................................................................................62
16.15 "/dev/tty? Device or resource busy"...........................................................................................63
16.16 "Input/output error" from setserial, stty, pppd, etc......................................................................64
16.17 "LSR safety check engaged"........................................................................................................64
16.18 Overrun errors on serial port........................................................................................................64
16.19 Port gets characters only sporadically..........................................................................................64
16.20 Troubleshooting Tools.................................................................................................................64
16.21 Almost all characters are wrong; Many missing or many extras.................................................65
17. Interrupt Problem Details................................................................................................................65
17.1 Types of interrupt problems...........................................................................................................65
17.2 Symptoms of Mis-set or Conflicting Interrupts.............................................................................65
17.3 Mis-set Interrupts..........................................................................................................................66
17.4 Interrupt Conflicts.........................................................................................................................67
17.5 Resolving Interrupt Problems........................................................................................................67
18. What Are UARTs? How Do They Affect Performance?...............................................................68
18.1 Introduction to UARTS.................................................................................................................68
18.2 Two Types of UARTs....................................................................................................................68
18.3 FIFOs............................................................................................................................................69
18.4 Why FIFO Buffers are Small.........................................................................................................69
18.5 UART Model Numbers..................................................................................................................70
19. Pinout and Signals..........................................................................................................................70
19.1 Pinout of 9-pin and 25-pin serial connectors.................................................................................70
19.2 Signals May Have No Fixed Meaning...........................................................................................71
19.3 Cabling Between Serial Ports.......................................................................................................71
19.4 RTS/CTS and DTR/DSR Flow Control........................................................................................72
The DTR and DSR Pins..................................................................................................................73
19.5 Preventing a Port From Opening...................................................................................................73
20. Voltage Waveshapes.......................................................................................................................73
20.1 Voltage for a Bit.............................................................................................................................73
20.2 Voltage Sequence for a Byte.........................................................................................................74
20.3 Parity Explained............................................................................................................................74
20.4 Forming a Byte (Framing).............................................................................................................74
20.5 How "Asynchronous" is Synchronized..........................................................................................75
21. Other Serial Devices (not async RS-232).......................................................................................75
21.1 Successors to RS-232....................................................................................................................75
21.2 EIA-422-A (balanced) and EIA-423-A (unbalanced)....................................................................75
21.3 EIA-485..........................................................................................................................................76
21.4 EIA-530..........................................................................................................................................76
21.5 EIA-612/613..................................................................................................................................76
21.6 The Universal Serial Bus (USB)....................................................................................................76
21.7 Firewire..........................................................................................................................................77
21.8 MIDI..............................................................................................................................................77
21.9 Synchronization & Synchronous..................................................................................................77
Defining Asynchronous vs Synchronous........................................................................................77
Synchronous Communication.........................................................................................................78
22. Other Sources of Information..........................................................................................................78
22.1 Books.............................................................................................................................................78
Serial HOWTO
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