HP 3336A Operating Manual page 39

Operation
3-111. Controller. The device that directs which device will talk and which device or devices
will listen is the CONTROLLER. The system controller (usually a calculator or computer) is
the active controller most of the time. However, it may direct another device to become the
active controller. The system controller is the only device which can unconditionally assume
control of the bus.
3-112. Addressing. The active controller directs which device will talk and which device or
devices will listen by specifically ADDRESSING those devices. Each device has a talk ad-
dress and a listen address. Therefore, when a controller addresses a device, it also specifies
whether the device will talk or listen. Some controllers require a decimal equivalent of the
talk and listen addresses, called the DEVICE ADDRESS. The factory presets the device ad-
dress (automatically assigning talk and listen addresses) to:
Device Address 4
Talk Address D
Listen Address $
The device address may be changed if desired (see Section II of this manual). Actually, there
is no reason to change it unless another device with the same address is added to the system.
3-113. Abridged Description of the HP-IB.
3-114. The HP-IB consists of 16 active signal lines that are used to interconnect up to 15
devices (e.g., instruments). The 16 signal lines are organized according to function. The
catagories are DATA, HANDSHAKE, and GENERAL INTERFACE MANAGEMENT
lines. The structure of the HP-IB is illustrated in Figure 3-2.
3-115. Data Lines. Eight DATA lines are used to carry instrument addresses, instrument
control instructions, measurement results and instruments status information in bit parallel,
byte serial form. Ordinarily, a seven bit ASCII code represents each byte of DATA. The
eighth bit is available for parity checking. DATA is sent over the DATA lines in both direc-
tions.
(e.g. calculator) (e.g. digital voltmeter ) (e.g. signal generator) (e.g. tape reader)
DEVICE A DEVICE B : DEVICE C DEVICE D
TALKS, LISTENS, TALKS AND LISTENS LISTENS ONLY TALKS ONLY
AND CONTROLS
Ltt +14 Saeeeee' i
ttt (te
«7
BUS MANAGEMENT
(5 signal lines)
HANDSHAKE
(3 signal lines) DATA INPUT OUTPUT
(8 signal lines)
Figure 3-2. General interface Management Lines.
Model 3336A/B/C
TOOTHER DEVICES
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