AM186ES Advanced Micro Devices, AM186ES Datasheet - Page 137

• Manufacturer Part Number: AM186ES
• Description: microcontrollers provide a low-cost/ high-performance solution for embedded system designers who wish to use the x86 architecture.
• Manufacturer: Advanced Micro Devices

Bit 1: Start/Stop DMA Channel (ST)—The DMA channel is started when the start bit is
set to 1. This bit can be modified only when the CHG bit is set to 1 during the same register
write. This bit is 0 after processor reset.
Bit 0: Byte/Word Select (B/W)—On the Am186ES microcontroller, when B/W is set to 1,
word transfers are selected. When B/W is set to 0, byte transfers are selected. Word
transfers are not supported on the Am188ES microcontroller. Only byte transfers are
supported when either the source or the destination bus width is 8 bits.
9.3.2
Serial Port/DMA Transfers
The Am186ES and Am188ES microcontrollers have the added feature of being able to
DMA to and from the serial ports. This is accomplished by programming the DMA controller
to perform transfers between a data buffer (located either in memory or I/O space) and a
serial port peripheral control register (SP0TD, SP1TD, SP0RD, or SP1RD). It is important
to note that when a DMA channel is in use by a serial port, the corresponding external DMA
request signal is deactivated.
For DMA to the serial port, the transmit data register address, either I/O mapped or memory
mapped, should be specified as a byte destination for the DMA by writing the address of
the register into the DMA destination low and DMA destination high registers. The
destination address (the address of the transmit data register) should be configured as a
constant throughout the DMA operation. The serial port transmitter acts as the
synchronizing device so the DMA channel should be configured as destination
synchronized.
For DMA from the serial port, the receive data register address, either I/O mapped or
memory mapped, should be specified as a byte source for the DMA by writing the address
of the register into the DMA Source and DMA Source High registers. The source address
(the address of the receive data register) should be configured as a constant throughout
the DMA. The serial port receiver acts as the synchronizing device so the DMA channel
should be configured as source synchronized.
DMA Controller
9-5