The IEEE-488 standard allows up to 15 devices to be interconnected on one bus. Each device is assigned a unique primary address, ranging from 0-30, by setting the address switches on the device. A secondary address may also be specified, ranging from 0-30. See the device documentation for more information on how to set the device primary and optional secondary address.
In the HTBasic statements that access the bus, a device selector is used to specify the interface select code, the primary device address, and the optional secondary device address. The default IEEE-488 interface select code is 7. The default primary address of the system controller is 21. The following examples demonstrate how the interface and device addresses are specified.
Device Selectors
ISC code
Pri. Add
Sec. Add
705
7
5
none
72501
7
25
1
1207
12
7
none
100412
10
4
12
The primary address of the IEEE-488 board can be read using the STATUS statement and changed with the CONTROL statement. Bits 0-4 of register three specify the primary address
.
STATUS 7,3; Pri_add !Read Primary Address
CONTROL 7,3; Pri_add !Set Primary Address
A discussion of the CONTROL and STATUS statements is given later in this section.
