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Programmable Interrupt Controllers
The 80C186EC utilizes two 8259A compatible Pro-
grammable Interrupt Controllers (PIC) to manage
both internal and external interrupts The 8259A
modules are configured in a master slave arrange-
ment
Seven of the external interrupt pins INT0 through
INT6 are connected to the master 8259A module
The eighth external interrupt pin INT7 is connected
to the slave 8259A module
There are a total of 11 internal interrupt sources
from the integrated peripherals 4 Serial 4 DMA and
3 Timer Counter
Timer Counter Unit
The 80C186EC Timer Counter Unit (TCU) provides
three 16-bit programmable timers Two of these are
highly flexible and are connected to external pins for
external control or clocking The third timer is not
connected to any external pins and can only be
clocked internally However it can be used to clock
the other two timer channels The TCU can be used
to count external events time external events gen-
erate non-repetitive waveforms or generate timed in-
terrupts
Serial Communications Unit
The 80C186EC Serial Communications Unit (SCU)
contains two independent channels Each channel is
identical in operation except that only channel 0 is
directly supported by the integrated interrupt control-
ler (the channel 1 interrupts are routed to external
interrupt pins) Each channel has its own baud rate
generator and can be internally or externally clocked
up to one half the processor operating frequency
Both serial channels can request service from the
DMA unit thus providing block reception and trans-
mission without CPU intervention
Independent baud rate generators are provided for
each of the serial channels For the asynchronous
modes the generator supplies an 8x baud clock to
both the receive and transmit shifting register logic
A 1x baud clock is provided in the synchronous
mode
DMA Unit
The four channel Direct Memory Access (DMA) Unit
is comprised of two modules with two channels
each All four channels are identical in operation
DMA transfers can take place from memory to mem-
ory I O to memory memory to I O or I O to I O
80C186EC 188EC 80L186EC 188EC
DMA requests can be external (on the DRQ pins)
internal (from Timer 2 or a serial channel) or soft-
ware initiated
The DMA Unit transfers data as bytes only Each
data transfer requires at least two bus cycles one to
fetch data and one to deposit The minimum clock
count for each transfer is 8 but this will vary depend-
ing on synchronization and wait states
Chip-Select Unit
The 80C186EC Chip-Select Unit (CSU) integrates
logic which provides up to ten programmable chip-
selects to access both memories and peripherals In
addition each chip-select can be programmed to
automatically insert additional clocks (wait states)
into the current bus cycle and or automatically ter-
minate a bus cycle independent of the condition of
the READY input pin
I O Port Unit
The I O Port Unit on the 80C186EC supports two
8-bit channels and one 6-bit channel of input output
or input output operation Port 1 is multiplexed with
the chip select pins and is output only Port 2 is mul-
tiplexed with the pins for serial channels 1 and 2 All
Port 2 pins are input output Port 3 has a total of 6
pins four that are multiplexed with DMA and serial
port interrupts and two that are non-multiplexed
open drain I O
Refresh Control Unit
The Refresh Control Unit (RCU) automatically gen-
erates a periodic memory read bus cycle to keep
dynamic or pseudo-static memory refreshed A 9-bit
counter controls the number of clocks between re-
fresh requests
A 12-bit address generator is maintained by the RCU
and is presented on the A12 1 address lines during
the refresh bus cycle Address bits A19 13 are pro-
grammable to allow the refresh address block to be
located on any 8 Kbyte boundary
Watchdog Timer Unit
The Watchdog Timer Unit (WDT) allows for graceful
recovery from unexpected hardware and software
upsets The WDT consists of a 32-bit counter that
decrements every clock cycle If the counter reach-
es zero before being reset the WDTOUT pin is
7
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