3023

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3023 is the Megalink interface.

Introduction

Megalink is designed according to the ISO 3309 standard, providing you with Point-to-point serial communication links, using HDLC protocol. It can operate in half or full duplex mode on point-to-point line. Multidrop requires external equipment.

Megalink may operate up to 983 Kbaud in a high throughput mode where retransmissions are avoided. This is achieved by using a busy line (requires an extra pair of wires in each direction in addition to the X.21 defined lines. This mode is easiest using a Megalink to Megalink computer link. Operation without busy lines is possible below 307 Kbaud.

It is recommended that the Megalink interface have the highest priority.

Switches and indicators

This card has three thumbwheel switches, from the top of the card

  • TH1 - baud rate selection
    • 0 - 307.2 kbps
    • 3 - 1.2 kbps
    • 6 - 9.6 kbps
    • 7 - 38.4 kbps
    • 8 - 153.6 kbps
    • 9 - 76.8 kbps
    • 11 - 19.2 kbps
    • 13 - 4.8 kbps
    • 14 - 2.4 kbps

settings not specified overlap with the specified settings. Baud rate selection is only relevant if the source oscillator switches are set to "baud rate via TH1".

  • TH3 - device register address and ident code
    • 0 - megalink 1 - device address 1640-1647 (octal) - ident code 150 (octal)
    • 1 - megalink 2 - device address 1660-1677 (octal) - ident code 151 (octal)
    • 2 - megalink 3 - device address 1700-1717 (octal) - ident code 152 (octal)
    • 3 - megalink 4 - device address 1720-1737 (octal) - ident code 153 (octal)
    • 4 - megalink 5 - device address 1740-1757 (octal) - ident code 154 (octal)
    • 5 - megalink 6 - device address 1760-1777 (octal) - ident code 155 (octal)
  • TH2 - autoload device numbers
    • 0 - N/A - device address 1600-1603 (not allowed)
    • 1 - autoload 1 - device address 1604-1607 (octal)
    • 2 - autoload 2 - device address 1610-1613 (octal)
    • 3 - autoload 3 - device address 1614-1617 (octal)
    • 4 - autoload 4 - device address 1620-1623 (octal)
    • 5 - autoload 5 - device address 1624-1627 (octal)
    • 6 - autoload 6 - device address 1630-1633 (octal)
    • 7 - autoload 7 - device address 1634-1637 (octal)

several other switches, labeled by their location

  • switch 26G - source oscillator selection
    • 6:on, 5:on, 4:off, 3:off, 2:on, 1:x - special 983 kbps, normal operation
    • 6:off, 5:on, 4:off, 3:on, 2:on, 1:x - baud rate via TH1
    • 6:off, 5:on, 4:on, 3:off, 2:on, 1:x - special 614.4 kbps

The switches are numbered 6,5,4,3,2,1 from left to right. An "x" indicates irrelevant (don't care) for that switch. Some switches with special meaning

  • 5:on - normal operation, processor clock enabled
  • 5:off - processor clock disabled (only used for card tester)
  • 2:on - normal operation, baud rate oscillator enabled
  • 2:off - baud rate oscillator disabled (only used for card tester)

end of switch 26G.

  • switch 17G - autoload function selection
  • 4:off, 3:off, 2:off, 1:off - normal operation, autoload function disabled
  • 4:off, 3:on, 2:on, 1:on - only if remote load from line is used
  • switch 13A - enable / disable BUSY
    • 4:x, 3:x, 2:off, 1:on - normal operation, BUSY enabled
    • 4:x, 3:x, 2:on, 1:off - BUSY disabled

x = irrelevant

and one indicator (lowest on the card)

  • transmission clock - yellow LED - lights up when transmission clock is not running

Connectors

The A and B connectors are used for I/O, the C connector is used for the ND-100 Bus.

I/O Devices on the card

none?

Modem connection

The electrical connection for a modem is V.11 (= X.27 = RS-422).

Programming

The Megalink DMA is operated by placing control information in a buffer memory, and the writing the address of this buffer - the LIST POINTER - to the Megalink module together with one of eight commands. The module will then perform the proper action. A command must be completed before a new command is issued. The only exception is the Device Clear sequences which may be initiated any time.

Commands

The 8 commands are

  • 0 - Device Clear
  • 1 - Initialize
  • 2 - Receiver Start
  • 3 - Receiver Continue
  • 4 - Transmitter Start
  • 5 - Dump Data Module
  • 6 - Dump Register(s)
  • 7 - Load Register(s)

ND sales number

  • ND 734 Megalink Interface for ND-100

References