20-bit Adder/Subtractor
Adder Control
Logic
Timer Request
DRQ1/Serial Port
20
Request
Selection
Logic
DRQ0/Serial Port
Transfer Counter Ch. 1
Destination Address Ch. 1
Source Address Ch. 1
Transfer Counter Ch. 0
DMA
Control
Logic
Destination Address Ch. 0
Source Address Ch. 0
Interrupt
Request
Channel Control Register 1
Channel Control Register 0
20
16
Internal Address/Data Bus
Figure 13. DMA Unit Block Diagram
ASYNCHRONOUS SERIAL PORT
The Am186ER and Am188ER microcontrollers provide
an asynchronous serial port. The asynchronous serial
port is a two-pin interface that permits full-duplex bidi-
rectional data transfer. The asynchronous serial port
supports the following features:
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.
DMA Transfers through the Serial Port
The DMA channels can be directly connected to the
asynchronous serial port. DMA and serial port transfer
is accomplished by programming the DMA controller to
perform transfers between a memory or I/O space and
a serial port transmit or receive register. For more infor-
mation see the DMA control register descriptions in the
Am186ER and Am188ER Microcontrollers User’s Man-
ual, order #21684.
n Full-duplex operation
n 7-bit or 8-bit data transfers
n Odd, even, or no parity
n 1 or 2 stop bits
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.
SYNCHRONOUS SERIAL INTERFACE
The synchronous serial interface (SSI) enables the
Am186ER and Am188ER microcontrollers to communi-
cate with application-specific integrated circuits (ASICs)
that require reprogrammability but are short on pins.
This four-pin interface permits half-duplex, bidirectional
data transfer at speeds of up to 25 Mbit/s.
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 using the se-
rial port are supported.
Unlike the asynchronous serial port, the SSI operates
in a master/slave configuration. The Am186ER and
Am188ER microcontrollers are the master ports.
The serial port generates one interrupt for any of three
serial port events—transmit complete, data received,
and receive error.
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
The serial port can be used in power-save mode, but
the software must adjust the transfer rate to correctly
56
Am186TMER and Am188TMER Microcontrollers Data Sheet
AMD [ AMD ]
