P R E L I M I N A R Y
entire memory map can be set to 16-bit or 8-bit or
Enhanced Refresh Control Unit
mixed between 8-bit and 16-bit based on the USIZ,
LSIZ, MSIZ, and IOSIZ bits in the AUXCON register.
The refresh control unit (RCU) is enhanced with two
additional bits in the refresh counter to allow for longer
refresh periods. The address generated during a
refresh has been fixed to FFFFFh. When either bank of
DRAM is enabled and the RCU is enabled, a CAS-
before-RAS refresh will be generated based on the
time period coded into the refresh counter.
Improved External Bus Master Support
When the bus is arbitrated away from the Am186ED/
EDLV microcontrollers using the HOLD pin, the chip
selects are driven High (negated) and then held High
with an internal ~10-kohm pullup. This allows external
bus masters to assert the chip selects by externally
pulling them Low, without having to combine the chip
selects from the Am186ED/EDLV microcontrollers and
the external bus master in logic external to the
Am186ED/EDLV microcontrollers. This internal pullup
is activated for any bus arbitration, even if the pin is
being used as a PIO input.
Option to Overlap DRAM with PCS
The peripheral chip selects (PCS0–PCS6) can overlap
DRAM blocks with different wait states without external
or internal bus contention. The RAS0 or RAS1 will
assert along with the appropriate PCS. The UCAS and
LCAS will not assert, preventing the DRAM from writing
erroneously or driving the data bus during a read. The
PCS must have the same or higher number of wait
states than the DRAM. The PCS bus width will be
determined by the LSIZ or USIZ bus widths as
programmed in the AUXCON register.
PSRAM Controller Removed
The PSRAM mode found on the Am186ES/ESLV
microcontrollers has been removed and replaced with
a DRAM controller. This includes removal of the variant
PSRAM LCS timing and refresh strobe on MCS3.
Additional Serial Port Mode for DMA
Support of 9-bit Protocols
A mode 7 was added to the serial port which enhances
the direct memory access (DMA) support for 9-bit
protocols. Using mode 2, the serial port can be
programmed to interrupt only if the 9th bit is set,
ignoring all 9th bit cleared byte receptions. Mode 3
receives all bytes, whether the 9th bit is set or cleared.
Mode 7 also receives all bytes whether the 9th bit is set
or cleared, but now an interrupt is generated when the
9th bit is set. This allows the DMA to service all
receptions, but also allows the CPU to intervene when
the trailer (9th bit set) is received. In all modes using
DMA, the interrupts other than transmitter ready and
character received interrupts can still be generated.
This allows the DMA to handle the standard sending
and receiving characters while the CPU can intervene
when a non-standard event (e.g., framing error)
occurs.
Option to Boot from 8- or 16-bit Memory
The Am186ED/EDLV microcontrollers can boot from 8-
or 16-bit-wide non-volatile memory, based on the state
of the S2/BTSEL pin. If S2/BTSEL is pulled High or left
floating, an internal pullup sets the boot mode option to
16-bit. If S2/BTSEL is pulled resistively Low during
reset, the boot mode option is for 8-bit. The status of
the S2/BTSEL pin is latched on the rising edge of reset.
If the 8-bit boot option is selected, the width of the
memory region associated with UCS can be changed
in the AUXCON register. This allows for cheaper 8-bit-
wide memory to be used for booting the
microcontroller, while speed-critical code and data can
be executed from 16-bit-wide lower memory. Eight-bit
or 16-bit-wide peripherals can be used in the memory
area between LCS and UCS or in the I/O space. The
Am186ED/EDLV Microcontrollers
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AMD [ AMD ]
