Black Box IC026A-R2, IC026AE-R2 6.8 More on Service Requests

60

RS-232↔IEEE 488 INTERFACE CONVERTER

6.7.12 T

AKE

C

ONTROL

(TCT)

This command passes bus control responsibilities from the current Controller

to another device which has the ability to control. ($09 )

6.7.13 S

ECONDARY

C

OMMAND

G

ROUP

(SCG)

These are any one of the 32 possible commands (0 to 31) in this group. They

must immediately follow a talk or listen address. ($60 to $7F)

6.7.14 P

ARALLEL

P

OLL

C

ONFIGURE

(PPC)

For devices capable of performing a Parallel Poll, this command determines

which data bit they are to assert in response to a Parallel Poll ($05)

6.7.15 P

ARALLEL

P

OLL

U

NCONFIGURE

(PPU)

This disables all devices from responding to a Parallel Poll. ($15)

6.8 More on Service Requests

Most of the commands covered, both uniline and multiline, are the

responsibility of the Active Controller to send and the bus devices to

recognize. Most of these happen routinely by the interface and are totally

transparent to the system programmer. Other commands are used directly by

the user to provide optimum system control. Of the uniline commands, SRQ

is very important to the test system, and the software designer has easy access

to this line by most devices. Service Request is the method by which a bus

device can signal to the Controller that an event has occurred. It is similar to

an interrupt in a microprocessor-based system.

Most intelligent bus peripherals have the ability to assert SRQ. A DMM might

assert it when its measurement is complete, if its input is overloaded or for

any of an assortment of reasons. A power supply might SRQ if its output has

current limited. This is a powerful bus feature that removes the burden from

the System Controller to periodically inquire, “Are you done yet?” Instead, the

Controller says, “Do what I told you to do and let me know when you’re done”

or “Tell me when something is wrong.”

Since SRQ is a single line command, there is no way for the Controller to

determine which device requested the service without additional information.

This information is provided by the multiline commands for Serial Poll and

Parallel Poll.

Contents

Main RS-232IEEE 488 INTERFACE CONVERTER EUROPEAN UNION DECLARATION OF CONFORMITY WARNING! Failure to follow these directives voids emission and immunity compliance. Page Page Page CONTENTS Contents RS-232IEEE 488 INTERFACE CONVERTER CONTENTS 1. Specifications WARNING! CHAPTER 1: Specifications CAUTION 2. Introduction 2.1 Description 2.2 Abbreviations CHAPTER 2: Introduction 3. Getting Started 3.1 Inspection 3.2 Configuration Figure 3-1. Factory-Default Settings. SW3 SW2 SW1 3.3 Serial Port Settings Figure 3-2. Switch SW1: Selecting the Serial Baud Rate. Figure 3-3. Switch SW1: Selecting the Serial Word Length (Data Bits). Figure 3-4. Switch SW1: Selecting the Serial Stop Bits. Figure 3-5. Switch SW2: Selecting the Serial Parity. Figure 3-6. Switch SW2: Enabling or Disabling Echo. Figure 3-7. Switch SW1: Selecting the Serial Handshake. 3.4 Selecting Terminator Substitution Figure 3-8. Switch SW2: Selecting the Serial Terminator. Figure 3-9. Switch SW3: Selecting the IEEE Bus Terminator. 3.5 Selecting the Mode Figure 3-10. Switch SW2: Selecting the Mode. 3.6 Selecting the IEEE Address Figure 3-11. Switch SW3: Selecting the IEEE Address. 3.7 Feature Selections Figure 3-12. Switch SW1: Enabling or Disabling Talk Back on Terminator in Controller Mode. Figure 3-13. Switch SW2: Enabling or Disabling Talk Back on Timeout in Controller Mode. Figure 3-14. Switch SW1: Enabling or Disabling SRQ on Last Serial Terminator in Peripheral Mode. 3.8 Serial Interface Figure 3-15. Selecting RS-232 or RS-422 Signal Levels. Figure 3-16. Rear View of the Interface Converters Serial Connector. Page Page 3.9 General CAUTION Page RS-232IEEE 488 INTERFACE CONVERTER 4.1 Controller-Mode (Serial to IEEE) Operation 4. Controller Operation 4.2 Serial and IEEE Terminator Substitution 4.3 IEEE Address Selection Figure 4-1. Switch SW3: Selecting the IEEE Address. 4.4 Talk-Back Features Figure 4-2. Switch SW1: Enabling or Disabling Talk-Back on Terminator. Figure 4-3. Switch SW2: Enabling or Disabling Talk-Back on Timeout. Page 4.5 Plotter Applications Figure 4-4. A PC-Based Graphics System. Figure 4-5. Selecting RS-232 Signal Levels. Figure 4-6. Interface Converter Settings for Use with HP 7580A Plotter on an IBM PC. SW2 SW3 SW1 Figure 4-7. MacPlot Configuration Screen. Figure 4-8. A Macintosh Based Graphics System. Interface Converter IEEE 488 RS-422 Page Figure 4-10. Interface Converter Settings for Use with HP 7580A Plotter on a Macintosh. Page 5. Peripheral Operation 5.1 Peripheral-Mode Operation 5.2 Serial and IEEE Input Buffers 5.3 IEEE Data Transfers Page RS-232IEEE 488 INTERFACE CONVERTER Figure 5-1. Switch SW1: Enabling or Disabling SRQ on Last Terminator. Figure 5-2. Serial Poll Status Byte. 5.4 Serial-Poll Status-Byte Register Page 5.5 Use of Serial and Bus Terminators 5.6 IEEE 488 Bus Implementation Page 5.7 IEEE Address Selection Figure 5-3. SW3 View for IEEE Address Selection. 6. IEEE 488 Primer 6.1 History 6.2 General Structure Page Figure 6-1. IEEE 488 Bus Structure. 6.3 Send It to My Address 6.4 Bus Management Lines 6.5 Handshake Lines Figure 6-2. IEEE Bus Handshaking. 6.6 Data Lines 6.7 Multiline Commands Page 6.8 More on Service Requests Page 7.1 Theory of Operation 7. Theory of Operation and Board Layout 7.2 Board Layout CHAPTER 7: Theory of Operation and Board Layout Figure 7-1. Component Layout of the Interface Converters Motherboard. Figure 7-2. Component Layout of the Interface Converters Serial I/O board. APPENDIX A: Sample Dumb-Terminal Program Appendix A. Sample Dumb-Terminal Program Appendix B. Character Codes and IEEE Multiline Messages Page Index INDEX