P R E L I M I N A R Y
t1
t2
t3
t4
Address
Phase
Data
Phase
CLKOUTA
A19–A0
Address
AD7–AD0
(Read)
Data
AD15–AD8
Address
Data
AD7–AD0
(Write)
LCS, or UCS
or
MCSx, PCSx
Figure 7. 8-Bit Mode—Read and Write with Address Bus Disable in Effect
BUS INTERFACE UNIT
The bus interface unit controls all accesses to external
peripherals and memory devices. External accesses
include those to memory devices, as well as those to
memory-mapped and I/O-mapped peripherals and the
peripheral control block. The Am186ED/EDLV micro-
controllers provide an enhanced bus interface unit with
the following features:
Further, system costs can be reduced for systems
using more than 64K of RAM by replacing SRAM with
less expensive DRAM.
Nonmultiplexed Address Bus
The nonmultiplexed address bus (A19–A0) is valid
one-half CLKOUTA cycle in advance of the address on
the AD bus. When used in conjunction with the modi-
fied UCS and LCS outputs and the byte-write enable
signals, the A19–A0 bus provides a seamless interface
to SRAM, and Flash EPROM memory systems.
n A nonmultiplexed address bus
n DRAM address multiplexing
n A static bus-sizing option for 8-bit and 16-bit mem-
ory and I/O
DRAM Address Multiplexing
n Separate byte write enables and CAS for High and
The A19–A0 address bus also provides the addresses
for the DRAM. When RAS0 or RAS1 asserts for a read
or write, all the address signals are valid. This allows
the DRAM to latch the odd addresses into the row ad-
dress. Before the UCAS and/or LCAS asserts, the odd
addresses A17–A1 change to reflect the even ad-
dresses. This allows the DRAM to latch in the even ad-
dresses into the column address. During a refresh
cycle, the entire A19–A0 address bus is stable but un-
defined. The internal address and that reflected on the
AD bus is all 1s. The DRAM pin interface is shown in
Table 6.
Low bytes
n Data strobe bus interface option
The standard 80C186/188 microcontroller multiplexed
address and data bus requires system interface logic
and an external address latch. On the Am186ED/EDLV
microcontrollers, new byte write enables, DRAM con-
trol logic, and a new nonmultiplexed address bus can
reduce design costs by eliminating this external logic.
The standard 80C186/188 microcontroller required ex-
ternal DRAM controller logic and DRAM address multi-
plex circuitry for interfacing to DRAM. On the
Am186ED/EDLV microcontrollers, the integrated
DRAM controller and internal address multiplexing can
reduce design costs by eliminating this external logic.
36
Am186ED/EDLV Microcontrollers
AMD [ AMD ]
