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A Local bus key (Figure 1-1) prevents devices with incompatible Local bus
signal levels from being installed in adjacent slots.
How Data is
Transferred
Data is transferred over the Local bus in units of blocks and frames (Figure
3-15). A frame consists of a series of blocks, and each block is a stream of
data bytes generated by a single device. If only one device is generating
data, then the block size and frame size are the same.
Handshake Protocol The LDAV8 and LREQ9 lines are used to handshake bytes of data across
the Local bus. Each data generating device asserts the LBLOCK11 flag with
the last data byte in the block. The device which generates the last block in
the frame asserts the LFRAME10 flag along with the LBLOCK11 flag.
Local Bus Modes There are several modes of operation used to generate or receive data over
the Local bus. The most common modes follow. The digitizer modes are
shown in bold and more information on these modes is contained in the
section "Setting the Local Bus Transfer Mode" on page 162.
Figure 3-15. HP E1429B Local Bus Data Transfer Protocol
Chapter 3 Understanding the HP E1429 Digitizer 157