adsp-21mod870-100 Analog Devices, Inc., adsp-21mod870-100 Datasheet - Page 7

• Manufacturer Part Number: adsp-21mod870-100
• Description: Internet Gateway Processor
• Manufacturer: Analog Devices, Inc.

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 in-
coming 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-21mod870 will remain in the idle
state for up to a maximum of n processor 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 3 shows a typical multichannel modem configuration
with the ADSP-21mod870. A line interface can be used to
connect the multichannel subscriber or client data stream to the
multichannel serial port of the ADSP-21mod870. The ADSP-
21mod870 can support 24 or 32 channels. The IDMA port of
the ADSP-21mod870 is used to give a host processor full access
to the internal memory of the ADSP-21mod870. This lets the
host dynamically configure the ADSP-21mod870 by loading code
and data into its internal memory. This configuration also lets
the host access server data directly from the ADSP-21mod870’s
internal memory. In this configuration, the ADSP-21mod870
should be put into host memory mode where Mode C = 1,
Mode B = 0 and Mode A = 1 (see Table II).
REV. 0
INTERFACE
CONTROL
T1, E1, PRI,
xDSL, ATM
CALL
LINE
ADSP-21mod870 FUNCTIONS
• V.34/56k MODEM
• V.17 FAX
• V.42, V.42bis, MNP2-5
21mod870
21mod870
Figure 4. External Crystal Connections
ADSP-
ADSP-
IDMA
IDMA
SP0
SP0
Figure 3. Network Access System
21mod870
21mod870
CLKIN
ADSP-
ADSP-
IDMA
IDMA
SP0
SP0
DSP
HOST BUS
DTMF DIALING
CALLER ID
HDLC PROTOCOL
XTAL
–7–
21mod870
21mod870
ADSP-
ADSP-
IDMA
IDMA
SP0
SP0
CLOCK SIGNALS
The ADSP-21mod870 can be clocked by either a crystal or a
TTL-compatible clock signal.
The CLKIN input cannot be halted, changed during operation,
or operated below the specified frequency during normal opera-
tion. The only exception is while the processor is in the power-
down state. For additional information, refer to Chapter 9,
ADSP-2100 Family User’s Manual, Third Edition, 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-21mod870 uses an input clock with a frequency
equal to half the instruction rate; a 26 MHz input clock yields a
19 ns processor cycle (which is equivalent to 52 MHz). Nor-
mally, instructions are executed in a single processor cycle. All
device timing is relative to the internal instruction clock rate,
which is indicated by the CLKOUT signal when enabled.
Because the ADSP-21mod870 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 capaci-
tors connected as shown in Figure 4. Capacitor values are de-
pendent on crystal type and should be specified by the crystal
manufacturer. A parallel-resonant, fundamental frequency,
microprocessor-grade crystal should be used.
A clock output (CLKOUT) signal is generated by the processor
at the processor’s cycle rate. This is enabled and disabled by the
CLKODIS bit in the SPORT0 Autobuffer Control Register.
CLKOUT
HOST FUNCTIONS
• MULTI-DSP CONTROL AND OVERLAY
• SERVICE 32 DSPs/HOST
• DATA PACKETIZING
MANAGEMENT
21mod870
21mod870
ADSP-
ADSP-
IDMA
IDMA
SP0
SP0
INTERNET
LAN OR
(2183)
HOST
ADSP-21mod870