HP 61010A Owner's Manual page 8

DIGITAL
INPUT
(BITS 015!
DIGITAL
OUTPUT
(BITS 0. IS)
IDAC
iDAV
QDAC
Figure 1-1. Digital I/O Block Diagram
Two basic operating modes are available for I/O data
transfers: synchronous and asynchronous. Synchronous
operation requires that some other instrument or hardware
source must communicate with the Digital I/O. This two-
way communication is referred to as ' 'handshaking'
When sending data to an external device, the Digital I/O
signals the external device that data is available. The
external device completes the handshake by returning a
signal that indicates it has received the information. When
receiving data from an external device, handshaking
requires that the external device must first signal the
Digital I/O that data is valid. To complete the handshake,
the Digital I/O will return a signal to indicate it has
successfully received the data.