P R E L I M I N A R Y
ASYNCHRONOUS SERIAL PORT
SYNCHRONOUS SERIAL INTERFACE
The Am186EM and Am188EM microcontrollers pro-
vide an asynchronous serial port. The asynchronous
serial port is a two-pin interface that permits full-duplex
bidirectional data transfer. The asynchronous serial
port supports the following features:
The synchronous serial interface (SSI) lets the
Am186EM and Am188EM microcontrollers communi-
cate with application-specific integrated circuits
(ASICs) that require reprogrammability but are short on
pins. This four-pin interface permits half-duplex, bidi-
rectional data transfer at speeds of up to 20 Mbits/sec.
n Full-duplex operation
n 7-bit or 8-bit data transfers
n Odd, even, or no parity
n 1 or 2 stop bits
Unlike the asynchronous serial port, the SSI operates
in a master/slave configuration. The Am186EM and
Am188EM microcontrollers are 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 are used to control and monitor the interface.
If additional RS-232 signals are required, they can be
created with available PIO pins. The asynchronous se-
rial port transmit and receive sections are double buff-
ered. Break character, framing, parity, and overrun
error detection are provided. Exception interrupt gener-
ation is programmable by the user.
Four-Pin Interface
The two enable pins SDEN1–SDEN0 can be used di-
rectly as enables for up to two peripheral devices.
The transmit/receive clock is based on the internal pro-
cessor clock, which is divided down internally to the se-
rial port operating frequency. The serial port permits 7-
bit and 8-bit data transfers. DMA transfers through the
serial port are not supported.
Transmit and receive operations are synchronized be-
tween the master (Am186EM and Am188EM micro-
controllers) and slave (peripheral) by means of the
SCLK output. SCLK is derived from the internal proces-
sor clock and is the processor clock divided by 2, 4, 8,
or 16.
The serial port generates one interrupt for any of three
serial port events—transmit complete, data received,
and error.
The serial port can be used in power-save mode, but
the software must adjust the transfer rate to correctly
reflect the new internal operating frequency and must
ensure that the serial port does not receive any infor-
mation while the frequency is being changed.
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Am186/188EM and Am186/188EMLV Microcontrollers
AMD [ AMD ]
