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Text File
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1992-04-27
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4KB
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77 lines
HARDWARE REBOOTER
=================
Purpose - reboot computer should the CD line not become high within 9 rings
(see note below). Relay contacts are connected to computer reset line. As
the hardware is right now, SYSOPS and assistant SYSOPS would know to hang up
on the ninth ring should the modem not answer (the system will reboot).
NOTE: Pin 1 is high on reset/initialization. First ring would bring pin 2
high. For this reason pin 9 would actually reboot the system on the eighth
ring.
+5VDC
│
│ ┌─┐ (5VDC REED RELAY)
├───┼─┼─┐
┴ ┌─┤ ├─┘ ┌───────[ +5 activates relay ]────────────┐
│ └─┼─┼─┐ └┐ │
├───┤ ├─┘ ┌──────────┼──────────────────────────┐ 10 5 │
│ └─┘ ┌─┼─┐ ┌┘ ┌──┬────┐ ┌───────┐ │ ┌──┐ │ │ │
+5VDC └────────────┘ │ └────┐ │ ╧ │ │ │ +5VDC │ │ │ ╧ │ │ │
│ │ │ │ │ │ │ │ │ │ │ │ │ │
┌──╫──╫──╫──╫──╫─╫─╫─┐ │┌──╫──╫──╫──╫──╫──╫──╫─╫─┐│ ┌──╫──╫──╫──╫──╫──╫──╫─╫─┐
│ 14 13 12 11 10 9 8 │ ││ 16 15 14 13 12 11 10 9 ││ │ 16 15 14 13 12 11 10 9 │
└┐ MC1489 │ │└┐ 4049 ││ └┐ 4017 │
┌┘QUAD LINE RECEIVER │ │┌┘ INVERTING HEX BUFFER ││ ┌┘DECADE COUNTER/DIVIDER │
│ 1 2 3 4 5 6 7 │ ││ 1 2--3 4--5 6 7 8 ││ │ 1 2 3 4 5 6 7 8 │
└──╫──╫──╫──╫──╫─╫─╫─┘ │└──╫──╫──╫──╫──╫──╫──╫─╫─┘│ └──╫──╫──╫──╫──╫──╫──╫─╫─┘
│ │ │ │ │ │ │ │ │ │ │ └─┤ │ │ │ │ │ │ │ │ │
│ │ │ │ │ │+5VDC │ │ │ └┐ ╧ │ │ │ │ │ │ │ │ ╧
┌┴─┐ │ ┌┴─┐ │ ╧ └──────┘ │ └───┼─────────┘ 6 2 1 3 7 8 4
│RI│ │ │CD│ │ └┐ ┌┘
└──┘ │ └──┘ └────────────────┼────┘
│ ┌┘
└───────────────────────┘
- CD resets 4017 decade counter (pin 15). Initialization string should
incorporate an AT&C0C1 to ensure the rebooter is reset (or it could reboot
the system when the next caller calls; the counter would keep going).
- 7805 Voltage regulator not show in schematic. Power supply is 9VDC
battery. 7805 supplies +5DC to all ICs and reed relay.
- Reed relay provides an isolated switch for motherboard reset pins.
NOTE: Unisys MDM-2400-USA modem activates relay on 4th ring. PP 9600SA modem
activates relay on 8th ring (as it's supposed to). Other modems not tested.
Unisys early activation is caused by a short pulse (not visible by eye) on RI
line just prior to pulse that is visible. This results in each ring counting
as two on the Unisys modem. Not a preferred setting because a caller could
end up rebooting the system a number of times trying to get on. If the
caller were to hang up on a ring with a multiple of 4 the computer would stay
in a state of reset.
Notes
=====
- Need to incorporate a capacitor on RI line so that this short pulse is not
interpreted as a separate logic high by quad line receiver. This would have
no effect on modems that don't provide the pulse while maintaining a high
logic level on those modems that do. Results - consistent, predictable
results.
- Relay stays closed until "activate ring"+1 (configurable on 4017, however
hard-wired for 9). 555 timer could eliminate this problem by keeping line
high for only 1 second. Currently, If a caller hangs up on ninth ring
computer stays in state of reset. Next callers first ring would allow
computer to reboot however if caller stays online for nine rings system would
remain in state of reset (not-likely occurrance)
- optic-isolator could be used to detect hi CD line(s) from other modem(s).
This line could be ANDed with 4017 to ensure system would not reboot while
other nodes had users. Considerable circuitry required to buffer 4017 state
until all CDs are low and to reset 4017 once relay activated (otherwise
computer system will stay in a state of reset).