P R E L I M I N A R Y
Interrupt requests are synchronized internally, and can
MCS3/RFSH/PIO25
be edge-triggered or level-triggered. To guarantee in-
terrupt recognition, the requesting device must con-
tinue asserting INT3 until the request is acknowledged.
INT3 becomes INTA1 when INT1 is configured in cas-
cade mode.
Midrange Memory Chip Select 3
(output, synchronous, internal pullup)
Automatic Refresh (output, synchronous)
MCS3—This pin indicates to the system that a memory
access is in progress to the fourth region of the
midrange memory block. The base address and size of
the midrange memory block are programmable. MCS3
is held High during a bus hold condition. In addition,
this pin has a weak internal pullup resistor that is active
during reset.
INTA1—When the microcontroller interrupt control unit
is operating in cascade mode or special fully-nested
mode, this pin indicates to the system that the micro-
controller needs an interrupt type to process the inter-
rupt request on INT1. In both modes, the peripheral
issuing the interrupt request must provide the micro-
controller with the corresponding interrupt type.
RFSH—This pin provides a signal timed for auto re-
fresh to PSRAM devices. It is only enabled to function
as a refresh pulse when the PSRAM mode bit is set in
the LMCS Register. An active Low pulse is generated
for 1.5 clock cycles with an adequate deassertion pe-
riod to ensure that overall auto refresh cycle time is
met. This pin is not three-stated during a bus hold condi-
tion.
IRQ—When the microcontroller interrupt control unit is
operating as a slave to an external master interrupt
controller, this pin lets the microcontroller issue an in-
terrupt request to the external master interrupt control-
ler.
INT4/PIO30
MCS2–MCS0
(MCS2/PIO24, MCS1/PIO15, MCS0/PIO14)
Maskable Interrupt Request 4 (input,
asynchronous)
This pin indicates to the microcontroller that an inter-
rupt request has occurred. If the INT4 pin is not
masked, the microcontroller then transfers program ex-
ecution to the location specified by the INT4 vector in
the microcontroller interrupt vector table.
Midrange Memory Chip Selects (output,
synchronous, internal pullup)
These pins indicate to the system that a memory ac-
cess is in progress to the corresponding region of the
midrange memory block. The base address and size of
the midrange memory block are programmable.
MCS2–MCS0 are held High during a bus hold condi-
tion. In addition, they have weak internal pullup resis-
tors that are active during reset.
Interrupt requests are synchronized internally, and can
be edge-triggered or level-triggered. To guarantee in-
terrupt recognition, the requesting device must con-
tinue asserting INT4 until the request is acknowledged.
NMI
LCS/ONCE0
Nonmaskable Interrupt (input, synchronous, edge-
sensitive)
Lower Memory Chip Select (output, synchronous,
internal pullup)
ONCE Mode Request 0 (input)
This pin indicates to the microcontroller that an inter-
rupt request has occurred. The NMI signal is the high-
est priority hardware interrupt and, unlike the INT4–
INT0 pins, cannot be masked. The microcontroller al-
ways transfers program execution to the location spec-
ified by the nonmaskable interrupt vector in the
microcontroller interrupt vector table when NMI is as-
serted.
LCS—This pin indicates to the system that a memory
access is in progress to the lower memory block. The
base address and size of the lower memory block are
programmable up to 512 Kbytes. LCS is held High dur-
ing a bus hold condition.
ONCE0—During reset this pin and ONCE1 indicate to
the microcontroller the mode in which it should operate.
ONCE0 and ONCE1 are sampled on the rising edge of
RES. If both pins are asserted Low, the microcontroller
enters ONCE mode; otherwise, it operates normally.
Although NMI is the highest priority interrupt source, it
does not participate in the priority resolution process of
the maskable interrupts. There is no bit associated with
NMI in the interrupt in-service or interrupt request reg-
isters. This means that a new NMI request can interrupt
an executing NMI interrupt service routine. As with all
hardware interrupts, the IF (interrupt flag) is cleared
when the processor takes the interrupt, disabling the
maskable interrupt sources. However, if maskable in-
terrupts are re-enabled by software in the NMI interrupt
service routine, via the STI instruction for example, the
fact that an NMI is currently in service will not have any
In ONCE mode, all pins assume a high-impedance
state and remain in that state until a subsequent reset
occurs. To guarantee that the microcontroller does not
inadvertently enter ONCE mode, ONCE0 has a weak in-
ternal pullup resistor that is active only during reset. This
pin is not three-stated during a bus hold condition.
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Am186/188EM and Am186/188EMLV Microcontrollers
AMD [ AMD ]
