P R E L I M I N A R Y
The asynchronous serial ports support the following
features:
PROGRAMMABLE I/O (PIO) PINS
There are 32 pins on the Am186ED/EDLV microcon-
trollers that are available as user-programmable I/O
signals. Table 2 on page 29 and Table 3 on page 29 list
the PIO pins. Each of these pins can be used as a user-
programmable input or output signal if the normal
shared function is not needed.
n Full-duplex operation
n Direct memory access (DMA) from the serial ports
n 7-bit, 8-bit, or 9-bit data transfers
n Odd, even, or no parity
n One stop bit
If a pin is enabled to function as a PIO signal, the pre-
assigned signal function is disabled and does not affect
the level on the pin. A PIO signal can be configured to
operate as an input or output with or without a weak
pullup or pulldown, or as an open-drain output.
n Long or short break character recognition
n Error detection
— Parity errors
— Framing errors
After power-on reset, the PIO pins default to various
configurations. The column titled Power-On Reset Sta-
tus in Table 2 on page 29 and Table 3 on page 29 lists
the defaults for the PIOs. The system initialization code
must reconfigure the PIOs as required.
— Overrun errors
— Break character recognition
n Hardware handshaking with the following select-
able control signals:
The A19–A17 address pins default to normal operation
on power-on reset, allowing the processor to correctly
begin fetching instructions at the boot address
FFFF0h. The DT/R, DEN, and SRDY pins also default
to normal operation on power-on reset.
— Clear-to-send (CTS)
— Enable-receiver-request (ENRX)
— Ready-to-send (RTS)
— Ready-to-receive (RTR)
Note that emulators use A19, A18, A17, S6, and UZI.
In environments where an emulator is needed, these
pins must be configured for normal function—not as
PIOs.
n DMA to and from the serial ports
n Separate maskable interrupts for each port
n Multidrop protocol (9-bit) support
If the AD15–AD0 bus override is enabled on power-on
reset, then S6/CLKDIV2 and UZI revert to normal oper-
ation instead of PIO input with pullup. If BHE/ADEN is
held Low during power-on reset, the AD15–AD0 bus
override is enabled.
n Independent baud rate generators
n Maximum baud rate of 1/16th of the CPU clock
n Double-buffered transmit and receive
n Programmable interrupt generation for transmit, re-
ceive, and/or error detection
When the PCS or MCS are used as PIO inputs (only)
and the bus is arbitrated, an internal pullup of ~10
kohms is activated, even if the pullup option for the PIO
is not selected.
DMA Transfers through the Serial Port
The DMA channels can be directly connected to the
asynchronous serial ports. 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. The two DMA
channels can support one serial port in full-duplex
mode or two serial ports in half-duplex mode. See the
DMA Control register descriptions in the Am186ED/
EDLV Microcontrollers User’s Manual, order# 21335A
for more information.
48
Am186ED/EDLV Microcontrollers
AMD [ AMD ]
