User`s manual

Backplane Interface Circuitry

The backplane interface circuitry allows you to access the backplane control

signals, data lines, address lines, trigger buses, and power supplies. The

backplane interface circuitry consists of the following functional groups:

• Address Lines and Register Decoding

• Data Bus Drivers

• Status Register

• ID Register

• Device Type Register

• Control Register

• DTACK, Interrupt and Control

• Backplane Signals and Voltages Available on the Module

• ECL Trigger Circuitry

The following sections discuss the backplane interface functional groups. Each

section includes a description, partial schematic, and timing diagrams (where

applicable). See Appendix B for schematics and complete parts list.

Note In the following hardware discussion, a high state (1) is indicated by a positive

voltage (usually + 5 V) and a low state (0) is indicated by 0 V ground) at the

specified signal point. A mnemonic suffixed with an asterisk (such as

WRITE*) indicates inverse logic (0 or low = true; 1 or high = false).

Address Lines and

Figure 2-19 shows the address line and register decoding circuitry. The

Agilent E1490C breadboard module is designed to be used as an A16/D16

device. As such, only backplane address lines A1 - A15 and data lines

D0 - D15 have been implemented on the module.

To address the module, the information present on backplane lines A6 - A13

must be identical to the logical address as set by address switch SP1 (0-7).

These eight bits allow up to 255 different VXIbus logical device addresses

to be selected in a VXIbus system.

If a logical address match occurs and IACK* is true, equality detector U18

produces a low at its output which enables U17. Next, equality detector

U17 compares the information on backplane lines A14, A15, AM0, AM1,

and AM3 - AM5 to a hardwired code of 11101101

. Since AM2 is not

examined, this hard-wired code will be a match if all 3 of the following

conditions are true:

• a hexadecimal code of either 29

or 2D

is present on AM0 - AM5.

• A14 and A15 are both high (1).

• LWORD is false (1).

32 Configuring the Agilent E1490C Chapter 2