ADSP-2104/ADSP-2109
Boot Mem or y Inter face
the number of wait states). T he instruction does not need to be
completed when the bus is granted; the processor will grant the
bus in between two memory accesses if an instruction requires
more than one external memory access.
Boot memory is an external 16K by 8 space, divided into eight
separate 2K by 8 pages. T he 8-bit bytes are automatically
packed into 24-bit instruction words by the processor, for
loading into on-chip program memory.
When the BR signal is released, the processor releases the BG
signal, re-enables the output drivers and continues program
execution from the point where it stopped.
T hree bits in the processors’ System Control Register select
which page is loaded by the boot memory interface. Another bit
in the System Control Register allows the forcing of a boot
loading sequence under software control. Boot loading from
Page 0 after RESET is initiated automatically if MMAP = 0.
T he bus request feature operates at all times, including when
the processor is booting and when RESET is active. If this
feature is not used, the BR input should be tied high (to VDD).
T he boot memory interface can generate zero to seven wait
states; it defaults to three wait states after RESET. T his allows
the ADSP-2104 to boot from a single low cost EPROM such as
a 27C256. Program memory is booted one byte at a time and
converted to 24-bit program memory words.
Low P ower ID LE Instr uction
T he IDLE instruction places the processor in low power state in
which it waits for an interrupt. When an interrupt occurs, it is
serviced and execution continues with instruction following
IDLE. T ypically this next instruction will be a JUMP back to
the IDLE instruction. T his implements a low-power standby
loop.
T he BMS and RD signals are used to select and to strobe the
boot memory interface. Only 8-bit data is read over the data
bus, on pins D8-D15. T o accommodate up to eight pages of
boot memory, the two MSBs of the data bus are used in the
boot memory interface as the two MSBs of the boot memory
address: D23, D22, and A13 supply the boot page number.
T he IDLE n instruction is a special version of IDLE that slows
the processor’s internal clock signal to further reduce power
consumption. T he reduced clock frequency, a programmable
fraction of the normal clock rate, is specified by a selectable
divisor, n, given in the IDLE instruction. T he syntax of the
instruction is:
T he ADSP-2100 Family Assembler and Linker allow the
creation of programs and data structures requiring multiple boot
pages during execution.
IDLE n;
T he BR signal is recognized during the booting sequence. T he
bus is granted after loading the current byte is completed. BR
during booting may be used to implement booting under control
of a host processor.
where n = 16, 32, 64, or 128.
T he instruction leaves the chip in an idle state, operating at the
slower rate. While it is in this state, the processor’s other
internal clock signals, such as SCLK, CLKOUT , and the timer
clock, are reduced by the same ratio. Upon receipt of an
enabled interrupt, the processor will stay in the IDLE state for
up to a maximum of n CLKIN cycles, where n is the divisor
specified in the instruction, before resuming normal operation.
Bus Inter face
T he ADSP-2104/ADSP-2109 can relinquish control of their
data and address buses to an external device. When the external
device requires control of the buses, it asserts the bus request
signal (BR). If the processor is not performing an external
memory access, it responds to the active BR input in the next
cycle by:
When the IDLE n instruction is used, it slows the processor’s
internal clock and thus its response time to incoming interrupts–
the 1-cycle response time of the standard IDLE state is in-
creased by n, the clock divisor. When an enabled interrupt is
received, the ADSP-21xx will remain in the IDLE state for up
to a maximum of n CLKIN cycles (where n = 16, 32, 64, or
128) before resuming normal operation.
•
T hree-stating the data and address buses and the PMS,
DMS, BMS, RD, WR output drivers,
•
•
Asserting the bus grant (BG) signal,
and halting program execution.
If the Go mode is set, however, the ADSP-2104/ADSP-2109
will not halt program execution until it encounters an instruc-
tion that requires an external memory access.
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
CLKIN cycles).
If the processor is performing an external memory access when
the external device asserts the BR signal, it will not three-state
the memory interfaces or assert the BG signal until the cycle
after the access completes (up to eight cycles later depending on
–8–
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