80C186XL 80C188XL
spond to bus cycles An offset map of the 256-byte
control register block is shown in Figure 3
Bus Interface Unit
The 80C186XL provides a local bus controller to
generate the local bus control signals In addition it
employs a HOLD HLDA protocol for relinquishing
the local bus to other bus masters It also provides
outputs that can be used to enable external buffers
and to direct the flow of data on and off the local
bus
The bus controller is responsible for generating 20
bits of address read and write strobes bus cycle
status information and data (for write operations) in-
formation It is also responsible for reading data
from the local bus during a read operation Synchro-
nous and asynchronous ready input pins are provid-
ed to extend a bus cycle beyond the minimum four
states (clocks)
The 80C186XL bus controller also generates two
control signals (DEN and DT R) when interfacing to
external transceiver chips This capability allows the
addition of transceivers for simple buffering of the
multiplexed address data bus
During RESET the local bus controller will perform
the following action
Chip-Select Ready Generation Logic
The 80C186XL contains logic which provides
programmable chip-select generation for both mem-
ories and peripherals In addition it can be
programmed to provide READY (or WAIT state) gen-
eration It can also provide latched address bits A1
and A2 The chip-select lines are active for all mem-
ory and I O cycles in their programmed areas
whether they be generated by the CPU or by the
integrated DMA unit
The 80C186XL provides 6 memory chip select out-
puts for 3 address areas upper memory lower
memory and midrange memory One each is provid-
ed for upper memory and lower memory while four
are provided for midrange memory
OFFSET
Relocation Register
FEH
DAH
DMA Descriptors Channel 1
D0H
Drive DEN RD and WR HIGH for one clock cy-
cle then float them
Drive S0– S2 to the inactive state (all HIGH) and
then float
CAH
DMA Descriptors Channel 0
C0H
Drive LOCK HIGH and then float
Float AD0– 15 (AD0– 8) A16– 19 (A9– A19) BHE
(RFSH) DT R
Drive ALE LOW
Drive HLDA LOW
RD QSMD UCS LCS MCS0 PEREQ MCS1
ERROR and TEST BUSY pins have internal pullup
devices which are active while RES is applied Ex-
cessive loading or grounding certain of these pins
causes the 80C186XL to enter an alternative mode
of operation
A8H
Chip-Select Control Registers
A0H
66H
Time 2 Control Registers
60H
5EH
Time 1 Control Registers
58H
56H
Time 0 Control Registers
50H
RD QSMD low results in Queue Status Mode
UCS and LCS low results in ONCE Mode
TEST BUSY low (and high later) results in En-
hanced Mode
3EH
Interrupt Controller Registers
20H
80C186XL PERIPHERAL
ARCHITECTURE
All the 80C186XL integrated peripherals are con-
trolled by 16-bit registers contained within an inter-
nal 256-byte control block The control block may be
mapped into either memory or I O space Internal
logic will recognize control block addresses and re-
Figure 3 Internal Register Map
The 80C186XL provides a chip select called UCS
for the top of memory The top of memory is usually
used as the system memory because after reset the
80C186XL begins executing at memory location
FFFF0H
5
ETC [ ETC ]
