AMD Am188TMER, Am186TMER user manual Synchronous Serial Interface 12-1

CHAPTER

12 SYNCHRONOUS SERIAL INTERFACE

12.1OVERVIEW

The synchronous serial interface enables the Am186ER and Am188ER microcontrollers to communicate with application-specific integrated circuits (ASICs) that require programmability but are short on pins. The four-pin interface permits half-duplex, bidirectional data transfer at speeds of up to 20 Mbit/s with a 40-MHz CPU clock.

Unlike the asynchronous serial port, the SSI operates in a master/slave configuration. The Am186ER and Am188ER microcontrollers operate as the master port.

The SSI interface provides four pins for communicating with system components: two enables (SDEN0 and SDEN1), a clock (SCLK), and a data pin (SDATA). Five registers (see Table 12-1)are used to control and monitor the interface.

νThe Synchronous Serial Status register (SSS) reports the current port status.

νThe Synchronous Serial Control register (SSC) sets the port clock rate and controls the enable signals.

νThere are two data transmit registers—the Synchronous Serial Transmit 0 register (SSD0) and the Synchronous Serial Transmit 1 register (SSD1)—but data is transmitted and received over a single pin (SDATA).

νThe Synchronous Serial Receive Register (SSR) holds data received over the SSI.

Table 12-1 Synchronous Serial Interface Register Summary

Offset from	Register
PCB	Mnemonic	Register Name
10h	SSS	Synchronous Serial Status
12h	SSC	Synchronous Serial Control
14h	SSD1	Synchronous Serial Transmit 1
16h	SSD0	Synchronous Serial Transmit 0
18h	SSR	Synchronous Serial Receive

Synchronous Serial Interface 12-1