CHAPTER 9 SYNCHRONOUS SERIAL I/O (SSIO) PORT

This device has a synchronous serial I/O (SSIO) port that shares pins with port 10. The SSIO provides two unidirectional serial communication channels or one synchronous bidirectional communication channel. The SSIO is compatible with most protocols because the serial clock is completely configurable. Paired, the SSIO channels can operate in a channel-select mode, allowing for communication in multiple-master systems without additional external hardware. Each SSIO channel can also perform handshaking transfers, which along with the PTS, provides unidirectional, multi-byte transfers with no CPU overhead. This chapter describes the SSIO port and explains how to program it.

9.1SSIO PORT OVERVIEW

The SSIO port has three modes of operation: standard, duplex, and channel-select. For singleslave, single-master systems requiring only one SSIO channel or two independent SSIO channels, use the standard mode of operation. In standard mode, each channel has a unique serial clock and data signal. For single-slave, single-master systems requiring two SSIO channels, use the duplex mode of operation. In duplex mode, the channels have unique serial data signals, but share a common clock signal. For systems with multiple masters or multiple slaves, use the channel-select mode of operation. Like duplex mode, in channel-select mode, the channels have unique serial data signals, but share a common clock signal. Channel-select mode provides an additional chan- nel-select signal designed for communicating in systems with multiple masters or multiple slaves.

In addition to three operating modes, the SSIO port can perform two types of data transfers: normal and handshaking. All modes support normal transfers, while only standard mode supports handshaking transfers. Normal transfers are compatible with most protocols because the serial clock is completely configurable. Handshaking transfers allow a slave device to notify the master that it is not ready for a transfer. “Normal Transfers (All Modes)” on page 9-9 and “Handshaking Transfers (Standard Mode Only)” on page 9-10 discuss these transfer types in detail.

9.1.1Standard Mode

In standard mode, the SSIO channels operate as two independent serial channels. Each channel contains one clock signal and one data signal. This mode is useful for systems in which unidirectional or half-duplex communication is acceptable. Half-duplex communication uses the same data signal for both transmissions and receptions. In standard mode, the channels can act as either master or slave and as either transmitter or receiver, resulting in the four configuration options shown in Figure 9-1.

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8XC196EA USER’S MANUAL

System with Multiple Slaves

System with Multiple Masters

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Figure 9-3. Channel-select Configuration Options

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