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1.1 root 1:
2:
3: terminal Technical Information terminal
4:
5:
6:
7:
8: This article describes how you can hook up a terminal to your
9: COHERENT system via a serial port. It also discusses common
10: problems that arise with this procedure, as diagnosed daily by
11: the technical support staff at Mark Williams Company. For
12: information on connecting a modem to your computer's serial port,
13: see the article mmooddeemm.
14:
15: ***** Hooking Up a Terminal to COHERENT *****
16:
17: This process is straightforward, but can be confusing if you
18: overlook any details. Typical problems include send/receive
19: confusion, baud rate confusion, and shell/no shell confusion.
20:
21: ***** Send/Receive Confusion *****
22:
23: A serial connection between your computer and a terminal requires
24: at least three wires: one each for pins 2, 3, and 7. These pins,
25: respectively, control send (TD), receive (RD), and signal-ground
26: (Gnd or SG). These pin numbers correspond to the 25-pin ``DB-
27: 25'' connectors used on most equipment. If your system has the
28: AT-style nine-pin ``DB-9'' connectors, you will need to wire to
29: the corresponding signals. See the Lexicon entry for RRSS-223322 for
30: details of the pin-outs for these two connectors.
31:
32: When hooking up a terminal to a serial port using a three-wire
33: connection, you must cross pins 2 and 3, so that each device's
34: send pin talks to the other device's receive pin. You can plug a
35: device called a ``null modem'' between the cable and the serial
36: port, to do this automatically. Unless someone has sat down and
37: taught you how to solder connectors, we strongly urge you to
38: purchase the necessary cable and null modem at your local
39: computer store or electronics shop.
40:
41: Note that the only symptom of a problem in the cable is that
42: nothing appears on your terminal when you type.
43:
44: ***** Baud-Rate Confusion *****
45:
46: The terminal and the computer must speak to each other at the
47: same _b_a_u_d _r_a_t_e. A typical symptom of baud-rate confusion is
48: garbage characters on the screen. When the wiring is wrong, you
49: see nothing; when the baud rate is wrong, you see something, but
50: nothing meaningful. You can fix baud-rate problems by using the
51: command ssttttyy to reset the baud rate on the port, or resetting the
52: baud rate on the terminal. For directions on how to reset the
53: baud rate for a port, see the Lexicon entry for ssttttyy.
54:
55: ***** The Old Shell Game *****
56:
57: Before a terminal is useful to you, you must _e_n_a_b_l_e the port into
58: which it is plugged. Enabling a port means that the COHERENT
59: system creates a shell for that port: this, in turn, means that
60: COHERENT prints a login prompt on the device plugged into that
61: port, and reads and processes interactively commands that are
62:
63:
64: COHERENT Lexicon Page 1
65:
66:
67:
68:
69: terminal Technical Information terminal
70:
71:
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73: entered from that port. The COHERENT system also restricts
74: permissions on all enabled serial ports, so that only the
75: superuser rroooott can read and write to the port. This prevents
76: other users who may be using the system from accessing the serial
77: port.
78:
79: Note that not all ports need be enabled: printer ports, for
80: example, should not be enabled; nor should you enable any port
81: whose device you want to accept data passively.
82:
83: When you boot the COHERENT system, it reads system file /eettcc/ttttyyss
84: and creates a shell for each serial port that needs one. One way
85: to enable a port is to log in as the superuser rroooott, then use a
86: text editor to change the port's entry in /eettcc/ttttyyss, as described
87: its Lexicon article. Finally, typing the command
88:
89:
90: kill quit 1
91:
92:
93: forces COHERENT to re-read /eettcc/ttttyyss and so create a shell for
94: the port. Note that doing this will ensure that the port is re-
95: enabled every time you boot.
96:
97: A better way to enable a port is to use the command eennaabbllee, as
98: described in its Lexicon article. For example, to put up a shell
99: on COM port /ddeevv/ccoomm11rr, log in as the superuser rroooott and type the
100: command:
101:
102:
103: /etc/enable com1r
104:
105:
106: ***** See Also *****
107:
108: mmooddeemm, RRSS-223322, ssttttyy, tteecchhnniiccaall iinnffoorrmmaattiioonn, tteerrmmccaapp, tteerrmmiioo, ttttyyss
109:
110: ***** Notes *****
111:
112: One final bit of hard-won wisdom: once you have something
113: working, write down what you did, and store it in a place where
114: you won't lose it. Note especially what connectors are where and
115: how they have been cabled together. It makes life easier just
116: knowing that you are looking for a female-to-female cable instead
117: of male-to-female or male-to-male. If you know whether to insert
118: a null modem, you are even better off.
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129:
130: COHERENT Lexicon Page 2
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