Synchronous Serial Interface 12-1
CHAPTER
12 SYNCHRONOUS SERIAL INTERFACE

12.1 OVERVIEW

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.
nThe Synchronous Serial Status register (SSS) reports the current port status.
nThe Synchronous Serial Control register (SSC) sets the port clock rate and controls the
enable signals.
nThere 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).
nThe Synchronous Serial Receive Register (SSR) holds data received over the SSI.
Table 12-1 Synchronous Serial Interface Register Summary
Offset from
PCB Register
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