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ADSP-2188N February 2001
This information applies to a product under development. Its characteristics and specifications are subject to change with-
out notice. Analog Devices assumes no obligation regarding future manufacturing unless otherwise agreed to in writing.
10 REV. PrA
• Support for crystal operation includes disabling the oscil-
lator to save power (the processor automatically waits
approximately 4096 CLKIN cycles for the crystal oscilla-
tor to start or stabilize), and letting the oscillator run to
allow 200 CLKIN cycle start-up.
• Power-down is initiated by either the power-down pin
(PWD) or the software power-down force bit. Interrupt
support allows an unlimited number of instructions to be
executed before optionally powering down. The
power-down interrupt also can be used as a nonmaskable,
edge-sensitive interrupt.
• Context clear/save control allows the processor to con-
tinue where it left off or start with a clean context when
leaving the power-down state.
•The RESET
pin also can be used to terminate
power-down.
• Power-down acknowledge pin indicates when the proces-
sor has entered power-down.
Idle
When the ADSP-2188N is in the Idle Mode, the processor
waits indefinitely in a low-power state until an interrupt
occurs. When an unmasked interrupt occurs, it is serviced;
execution then continues with the instruction following the
IDLE instruction. In Idle mode IDMA, BDMA and auto-
buffer cycle steals still occur.
Slow Idle
The IDLE instruction is enhanced on the ADSP-2188N to
let the processor’s internal clock signal be slowed, further
reducing power consumption. The reduced clock fre-
quency, a programmable fraction of the normal clock rate,
is specified by a selectable divisor given in the IDLE
instruction.
The format of the instruction is:
IDLE (N);
where n = 16, 32, 64, or 128. This instruction keeps the
processor fully functional, but operating at the slower clock
rate. While it is in this state, the processor’s other internal
clock signals, such as SCLK, CLKOUT, and timer clock,
are reduced by the same ratio. The default form of the
instruction, when no clock divisor is given, is the standard
IDLE instruction.
When the IDLE (n) instruction is used, it effectively slows
down the processor’s internal clock and thus its response
time to incoming interrupts. The one-cycle response time
of the standard idle state is increased by n, the clock divisor.
When an enabled interrupt is received, the ADSP-2188N
will remain in the idle state for up to a maximum of n pro-
cessor cycles (n = 16, 32, 64, or 128) before resuming
normal operation.
When the IDLE (n) instruction is used in systems that have
an externally generated serial clock (SCLK), the serial clock
rate may be faster than the processor’s reduced internal
clock rate. Under these conditions, interrupts must not be
generated at a faster rate than can be serviced, due to the
additional time the processor takes to come out of the idle
state (a maximum of n processor cycles).
SYSTEM INTERFACE
Figure 2 shows typical basic system configurations with the
ADSP-2188N, two serial devices, a byte-wide EPROM,
and optional external program and data overlay memories
(mode-selectable). Programmable wait state generation
allows the processor to connect easily to slow peripheral
devices. The ADSP-2188N also provides four external
interrupts and two serial ports or six external interrupts and
one serial port. Host Memory Mode allows access to the full
external data bus, but limits addressing to a single address
bit (A0). Through the use of external hardware, additional
system peripherals can be added in this mode to generate
and latch address signals.
Clock Signals
The ADSP-2188N can be clocked by either a crystal or a
TTL-compatible clock signal.
The CLKIN input cannot be halted, changed during oper-
ation, nor operated below the specified frequency during
normal operation. The only exception is while the processor
is in the power-down state. For additional information, refer
to the ADSP-218x DSP Hardware Reference, for detailed
information on this power-down feature.
If an external clock is used, it should be a TTL-compatible
signal running at half the instruction rate. The signal is con-
nected to the processor’s CLKIN input. When an external
clock is used, the XTAL input must be left unconnected.
The ADSP-2188N uses an input clock with a frequency
equal to half the instruction rate; a 40 MHz input clock
yields a 12.5 ns processor cycle (which is equivalent to 80
MHz). Normally, instructions are executed in a single pro-
cessor cycle. All device timing is relative to the internal
instruction clock rate, which is indicated by the CLKOUT
signal when enabled.
Because the ADSP-2188N includes an on-chip oscillator
circuit, an external crystal may be used. The crystal should
be connected across the CLKIN and XTAL pins, with two
capacitors connected as shown in Figure 3. Capacitor val-
ues are dependent on crystal type and should be specified
by the crystal manufacturer. A parallel-resonant, funda-
mental frequency, microprocessor-grade crystal should be
used.
A clock output (CLKOUT) signal is generated by the pro-
cessor at the processor’s cycle rate. This can be enabled and
disabled by the CLKODIS bit in the SPORT0 Autobuffer
Control Register.