MIR PUBLICATIONS COMPACTUS(LENDLNG SECTION)

DEPARTMENT OFNATIONAL RESOURCES

066770

NATIONAL DEVELOPMENTill BUREAU OF MINERAL RESOURCES,

•GEOLOGY AND GEOPHYSICS

1979/48

SIXTEEN CHANNEL DIGITAL MULTIPLEXER

BMR type XMM-1

A.B: DEVENISH

The information contained in this report has been obtained by the Department of NationUI Resourcessrt of the policy of the Australian Government to assist in the exploration and development of.al resources. It may not be published in any form or used in a company prospectus or statementput the permission in writing of the Director. Bureau of Mineral Resources, Geology and Geophysics.

•

1979/48

SIXTEEN CHANNEL DIGITAL MULTIPLEXER

BMR type XDM-1

A.B. DEVENISH

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Contents

•

•1. Introduction

2. Functional Descri -otion

3.^Unit Description

(i) Block Diagram

(ii) Tri-State Bus

(iii)Latch

(iv) Unit Select

(v) Channel Select

(vi) Busy

(vii) Device Flag

(viii)Power Supply

(ix) Bus Buffer

(x) Card Types

(xi) Software testing

(xii)Daisy Chaining

4.^Specifications

5. Use in VH-BMR aircraft

6. Use in magnetotelluric system

7.^Drawings and handbooks

(i) Circuit Schematic of Data hatch

(ii) Circuit schematic of Channel Select

(iii)Circuit Schematic of Bus Buffer

(iv) Circuit schematic of power supply.

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1. Sixteen Channel Digital Multiplexer

BMR Type XDM-1

1. Introduction

The HP 2100 series computers used for survey data acquisition

have nine input/output slots, some of which are used for such peripherals

as teletypes and tape units. Normally, each device outputting data to

the computer would require one input/output slot, which limits the number

of devices which could be connected to the computer. This problem can be

overcome by multiplexing a number of digital inputs into the one input/output

slot.

A decision was made by the ADP and Electronics Sections to design

a 16-channel 16-bit word multiplexer for use with the HP 2100 series

computers. Two units were constructed inihe first instance, one for thecomputer-based data acquisition system in BMR's Aerocommander survey

aircraft, the other for BMR's magnetotellurics system. The unit in the

survey aircraft inputted the altitude, 4 gamma-ray channels, magnetometer

readings, fiducial numbers and flight numbers. The unit in the magnetotelluric

system inputted the gain and filter settings of the E pre-amps, the H pre-amps,

and the post-amps. Some of the inputs from the magnetotelluric system

required voltage level translation to TTL. To allow for this, the option

of optically isolating each input was incorporated.

Three units have been constructed. Units have been used in the

Aerocommander survey aircraft and in the magnetotelluric system. Other units

will be used in the Twin-Otter aircraft and in the marine data acquisition

system to expand its input capacity to 32 channels.

2.

2. Function Description

The function of this unit is to receive 16-bit parallel

inputs from various input devices and output them, one 16-bit channel

at a time, to a HP 2100 series computer. There is a maximum of 16 input

channels, and a digital channel-select output from the computer determines

which input the computer will receive.

Up to eight units can be 'daisy chained' together to expand the

input capacity to 128 channels.^ •

The multiplexer provides for a busy device input which, if

activated, will disable the inputs to its internal latches.

Any one channel, and only one, can be linked to set the flag of

the computer I/O card.

All imputs and outputs are TTL compatible; the inputs may be

optically isolated.

DEVICE BUSY AND FLAG

16 INPUT CHANNELS.

(16 BI TS PERCHANNEL)

AS ABOVE

AS ABOVE

.-111110---DEVICE FLAG-0.---UNIT SELECT^(4 BITS)

MULTIPLEXER ^CHANNEL SELECT(4 BITS)DATA (16 BITS)

TO /0CARD IN

COMPUTER

MULTIPLEX ER

INTER-MULTIPLEXER CONNECTION

MULTIPLEXER

3. Unit Description

(I)^BLOCK DIAGRAM:

16 DECODE LINES_ONE FOR EACHCHANNEL.

OPTO- ISOLATORS. BUFFEREDLATCH.

8 BITS TO NEXT CHANNELAND UNIT SELECT.

3 .

•

(Note: The input data may be directly connected or optically isolated

from the data latches. If directly connected, the opto-isolators

are removed from their sockets and links put in.)

• (ii) Tri-State Bus

The outputs of all latches •in all units are connected to the

data bus. Which sixteen bits of data are valid on the bus depends on

which set of four latches is enabled by the channel and unit select

inputs.

4 .

4 BITSLATCH

16 DATA BITS

LATCH

ENABLE

4 BITSIIP^

4 BITSLATCH

LATCH

(iii) Latch

The input data for all channels are latched to the output by

means of a latch pulse. The latch pulse is generated in the computer by

the instructions:

STC^mpx

CLC^mpx

(iv) Unit Select

Bits 4-7 from the computer are used to determine which unit is

to be selected. A link has to be connected in the channel select card to

make the unit correspond to the chosen bit pattern. The unit select

decoder enables the channel select decoder for that unit.

(v) Channel Select

Bits 0-3 from the computer are used to select which output

channel is enabled onto the data bus.

( vi) Busy

The multiplexer may accept a busy signal from a device. This

signal disables the input to that device. If the busy channel is enabled,

only the previous stored reading of the input device will be put onto the

data bus.

41

DATA

BUS

4 BITS

5 .

(vii) Device Flag

41^ Any one device may be chosen to set the flag of the computer.

This is accomplished by installing a link on the appropriate data latch

card. Provision is made for selecting either logic state of the signal

41^input on the device flag line.

(viii) Power Supply

41^ Three types of power supply have been used in the multiplexers.

A 28 volt D.C. to 5 volt D.C. switching regulator type for aircraft use,

a 115 volt (50-400 Hz) A.C. to 5 volt D.C. for the magnetotelluric system, and a

41^standard 240V (50 Hz) A.C. to 5 Volt D.C. for other users.'

(ix) Bus Buffer

•^The data bus is buffered to the computer using open collector

buffers .. The device command signal from the computer is buffered by a

transistor to strobe all the data latches.

(x) Card Types

The unit contains 3 card types. They are:

(a) Channel Select card - This card enables the selected channel by

enabling the output onto the bus.

0^(b) Data latch card - Each of these. cards receives 16 data inputs

• from a device.. One of these cards is required for each device

• being multiplexed. The data inputs can either be direct or

optically coupled. For direct'coupling, the optc isolators are

removed from their sockets and wire bridges put in their place.

• (c) Bus buffer card - This card buffers the data bus going to the

•^computer and the device command 'signal going from the computer

to the device.

(Note: Cards have their card types Written on them).

6 .

(xi) Software Testing

The multiplexer can be tested by inserting a small program into

the computer and putting a known input into the various data inputs.

INPUTDATA

CPU

!MULTIPLEXER

A suitable program would be

START^LDA^X^Load the A register with memory

location X.

OTA^mpx^Output the A register to the select

code used with the multiplexer.

STC^mpx^These two instructions cause the latches

CLC^mpx^to strobe the input data.

LIB^mpx^Load the B register with what is on the

bus.

OTB^1^Output the B register to the switch

register.

JMP START^Jump back to start.

mpx is the select code of the I/O card used.

Memory location X^

7-4^3-0

unit select channel select

(xii) Daisy Chaining

The data bus, latch drive, device flag and lines for channel

select and unit select go to two other connectors to enable 'daisy

Chaining' of units.

INPUTS

CPU

4

MULTIPLEXER

MULTIPLEXER

INPUTS

7.

Up to 128 inputs may be on the data bus. This upper limit is due to the

electronic specifications of the tri-state latches.

Specifications

•-^Weight^-^6 kg

Size^-^24 x 9 x 48 cm

Supply voltage -^28 volt D.C.^4A max or 115V (50-400 Hz)

•^ A.C. or 240V (50 Hz) AC

Inputs^16^16 parallel bit data inputs.

TTL compatible.

busy line.

device flag.

Note: All inputs may be optically isolated. If the opto-isolators are

• used, the common line (Pin 1B) is taken to the logic high of the

device. If the opto-isolators are not used, the normi ground is

used as the logic common (Pin 24). The opto-isolators have to be

• removed and the following bridge put in.

8765

•1234

Outputs^ multiplexer/multiplexer connections.

data out to + ve true I/0 card.

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1 11 11 11 1 1111 1111rn^_____

Mu ILI e xerti-Multiplexer

'Channel 0

Connector positions

8 .

Rear Panel

,^16 Inputs

5.^Use in VH-BMR aircraft

The multiplexer is used in the survey aircraft system to connect

nine input channels to one computer I/O slot.

CHANNEL SELECTUNIT SELECTAND STROBE

CPU

MULTIPLEXER

I I ,1-

FLIGHT NUMBER

SCALERS( RADIOMETRIC COUNT)

FIDUCIAL NUMBER

ALTITUDEDIGITIZER

I MAGNETOMETER

DATA OUT 15 14 13 12 11 1098 765 432 10

0

9 .

•Channel. Select, Unit Select and input device correspondence

• Device^ Channel^Select^Unit Select

Magnetometer most significant digit^o

Magnetometer four least significant

digits

Altitude^ 2

• Fiducial Number^ 3

• Radiometric 1^ .4

0-^Radiometric 2^ 5

Radiometric 3^ .6

Radiometric 4^ 7

Flight number^ 10

6.^Use in the Magnetotelluric system

• The magneto—telluric data acquisition system records the 3 orthogonalmagnetic field components (11z,RX,Fry) of the electromagnetic radiation impinging onthe earth's surface and two -^, : resulting orthogonal electric field

components Ex,Ey) at the earth's surface.From these data the magneto—telluricparameters Cagniard resistivities t rotated resistivity tensors and phase anp:les,etc) are computed.•

In order to recover the actual values of these related fields

it is essential to correct the measurements using the transfer•characteristics of the amplifiers and filters used in making the

.measurements.

To do this the gain and filter settings are encoded and passed to

the multiplexer which outputs them to the computer. The computer then

stores them with the relevant measurements for subsequent correction.

•10.

GA IN AND FILTER SET Tti GS

4110---111111-

•MUX

CPUSTORAGE

DISC

PRE-AMP POST-AMPAND AND ADC •

FILTER FILTER

Channel Select, Unit Select and input correspondence

Device^ Channel Select Unit Select •Pre-amp gain and filter settings^Ex,Ey^optically

isolated

0 0

Hz,Hx,Hy optically

isolated

1 0 -•

Post-amp gain And filter setting 23 0 •4

Computer flag 5

7.^Drawings and Handbooks ^ •Four circuitschematics can be found in the back of this record.

The circuits are

Data Latch

Channel Select

Bus Buffer

Power Supply^ •

The 28 volt to 5 volt switching regulator is incorporated in the

unit used in the survey aircraft. The circuit diagram for it is given. •The units which run off 240 and 115 volt A.C. use commercial modular power

supplies.

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The handbooks for the unit contain parts lists and wiring lists

as well as circuit diagrams.

Handbooks can be found in the handbook master copy library in the

Enqineoring Serv 4_ces Branch and with each of the user groups,

•Printed by C. J. Thoupsom. Commonwealth Government Printer, Canberra