patch-2.1.67 linux/Documentation/networking/PLIP.txt

• Lines: 163
• Date: Sat Nov 29 10:33:18 1997
• Orig file: v2.1.66/linux/Documentation/networking/PLIP.txt
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.1.66/linux/Documentation/networking/PLIP.txt linux/Documentation/networking/PLIP.txt
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+PLIP: The Parallel Line Internet Protocol Device
+
+Donald Becker (becker@super.org)
+I.D.A. Supercomputing Research Center, Bowie MD 20715
+
+At some point T. Thorn will probably contribute text,
+Tommy Thorn (tthorn@daimi.aau.dk)
+
+PLIP Introduction
+-----------------
+
+This document describes the parallel port packet pusher for Net/LGX.
+This device interface allows a point-to-point connection between two
+parallel ports to appear as a IP network interface.
+
+What is PLIP?
+=============
+
+PLIP is Parallel Line IP, that is, the transportation of IP packages
+over a parallel port. In the case of a PC, the obvious choice is the
+printer port.  PLIP is a non-standard, but [can use] uses the standard
+LapLink null-printer cable [can also work in turbo mode, with a PLIP
+cable]. [The protocol used to pack IP packages, is a simple one
+initiated by Crynwr.]
+
+Advantages of PLIP
+==================
+
+It's cheap, it's available everywhere, and it's easy.
+
+The PLIP cable is all that's needed to connect two Linux boxes, and it
+can be build for very few bucks.
+
+Connecting two Linux boxes takes only a seconds decision and a few
+minutes work, no need to search for a [supported] netcard. This might
+even be especially important in the case of notebooks, where netcard
+are not easily available.
+
+Not requiring a netcard also means that apart from connecting the
+cables, everything else is software configuration [which in principle
+could be made very easy.]
+
+Disadvantages of PLIP
+=====================
+
+Doesn't work over a modem, like SLIP and PPP. Limited range, 15 m.
+Can only be used to connect three (?) Linux boxes. Doesn't connect to
+an exiting ethernet. Isn't standard (not even de facto standard, like
+SLIP).
+
+Performance
+==========
+
+PLIP easily outperforms ethernet cards....(ups, I was dreaming, but
+it *is* getting late. EOB)
+
+PLIP hardware interconnection
+-----------------------------
+
+PLIP uses several different data transfer methods.  The first (and the
+only one implemented in the early version of the code) uses a standard
+printer "null" cable to transfers data four bits at a time using
+data bit outputs connected to status bit inputs.
+
+The second data transfer method relies on both machines having
+bi-directional parallel ports, rather than output-only ``printer''
+ports.  This allows byte-wide transfers and avoids reconstructing
+nibbles into bytes, leading to much faster transfers.
+
+Parallel Transfer Mode 0 Cable
+==============================
+
+The cable for the first transfer mode is a standard
+printer "null" cable which transfers data four bits at a time using
+data bit outputs of the first port (machine T) connected to the
+status bit inputs of the second port (machine R).  There are five
+status inputs, and they are used as four data inputs and a clock (data
+strobe) input, arranged so that the data input bits appear as contiguous
+bits with standard status register implementation.
+
+A cable that implements this protocol is available commercially as a
+"Null Printer" or "Turbo Laplink" cable.  It can be constructed with
+two DB-25 male connectors symmetrically connected as follows:
+
+    STROBE output	1*
+    D0->ERROR	2 - 15		15 - 2
+    D1->SLCT	3 - 13		13 - 3
+    D2->PAPOUT	4 - 12		12 - 4
+    D3->ACK	5 - 10		10 - 5
+    D4->BUSY	6 - 11		11 - 6
+    D5,D6,D7 are   7*, 8*, 9*
+    AUTOFD output 14*
+    INIT   output 16*
+    SLCTIN	17 - 17
+    extra grounds are 18*,19*,20*,21*,22*,23*,24*
+    GROUND	25 - 25
+* Do not connect these pins on either end
+
+If the cable you are using has a metallic shield it should be
+connected to the metallic DB-25 shell at one end only.
+
+Parallel Transfer Mode 1
+========================
+
+The second data transfer method relies on both machines having
+bi-directional parallel ports, rather than output-only ``printer''
+ports.  This allows byte-wide transfers, and avoids reconstructing
+nibbles into bytes.  This cable should not be used on unidirectional
+``printer'' (as opposed to ``parallel'') ports or when the machine
+isn't configured for PLIP, as it will result in output driver
+conflicts and the (unlikely) possibility of damage.
+
+The cable for this transfer mode should be constructed as follows:
+
+    STROBE->BUSY 1 - 11
+    D0->D0	2 - 2
+    D1->D1	3 - 3
+    D2->D2	4 - 4
+    D3->D3	5 - 5
+    D4->D4	6 - 6
+    D5->D5	7 - 7
+    D6->D6	8 - 8
+    D7->D7	9 - 9
+    INIT -> ACK  16 - 10
+    AUTOFD->PAPOUT 14 - 12
+    SLCT->SLCTIN 13 - 17
+    GND->ERROR	18 - 15
+    extra grounds are 19*,20*,21*,22*,23*,24*
+    GROUND	25 - 25
+* Do not connect these pins on either end
+
+Once again, if the cable you are using has a metallic shield it should
+be connected to the metallic DB-25 shell at one end only.
+
+PLIP Mode 0 transfer protocol
+=============================
+
+The PLIP driver is compatible with the "Crynwr" parallel port transfer
+standard in Mode 0.  That standard specifies the following protocol:
+
+   send header nibble '8'
+   count-low octet
+   count-high octet
+   ... data octets
+   checksum octet
+
+Each octet is sent as
+	<wait for rx. '1'>	<send 0x10+(octet&0x0F)>
+	<wait for rx. '0'>	<send 0x00+((octet>>4)&0x0F)>
+
+To start a transfer the transmitting machine outputs a nibble 0x08.
+The raises the ACK line, triggering an interrupt in the receiving
+machine.  The receiving machine disables
+
+Restated:
+
+(OUT is bit 0-4, OUT.j is bit j from OUT. IN likewise)
+Send_Byte:
+   OUT := low nibble, OUT.4 := 1
+   WAIT FOR IN.4 = 1
+   OUT := high nibble, OUT.4 := 0
+   WAIT FOR IN.4 = 0