How Data is Transferred

A Local bus key (Figure 1-1) prevents devices with incompatible Local bus signal levels from being installed in adjacent slots.

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.

Figure 3-15. HP E1429B Local Bus Data Transfer Protocol

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.

Chapter 3

Understanding the HP E1429 Digitizer 157

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HP E1429A manual How Data is Transferred, HP E1429B Local Bus Data Transfer Protocol