Analog Devices ADSP-2181 - Manual (Page 10)

ADSP-2181/ADSP-2183
REV. 0 –10–
If the ADSP-2181/ADSP-2183 is performing an external
memory access when the external device asserts the BR signal,
then it will not three-state the memory interfaces or assert the
BG
signal until the processor cycle after the access completes.
The instruction does not need to be completed when the bus is
granted. If a single instruction requires two external memory ac-
cesses, the bus will be granted between the two accesses.
When the BR signal is released, the processor releases the BG
signal, reenables the output drivers and continues program ex-
ecution from the point where it stopped.
The bus request feature operates at all times, including when
the processor is booting and when RESET is active.
The BGH pin is asserted when the ADSP-2181/ADSP-2183 is
ready to execute an instruction but is stopped because the exter-
nal bus is already granted to another device. The other device
can release the bus by deasserting bus request. Once the bus is
released, the ADSP-2181/ADSP-2183 deasserts BG and BGH
and
executes the external memory access.
Flag I/O Pins
The ADSP-2181/ADSP-2183 has eight general purpose pro-
grammable input/output flag pins. They are controlled by two
memory mapped registers. The PFTYPE register determines the
direction, 1 = output and 0 = input. The PFDATA register is
used to read and write the values on the pins. Data being read
from a pin configured as an input is synchronized to the ADSP-
2181/ADSP-2183’s clock. Bits that are programmed as outputs
will read the value being output. The PF pins default to input
during reset.
In addition to the programmable flags, the ADSP-2181/ADSP-
2183 has five fixed-mode flags, FLAG_IN, FLAG_OUT, FL0,
FL1, and FL2. FL0-FL2 are dedicated output flags. FLAG_IN
and FLAG_OUT are available as an alternate configuration of
SPORT1.
BIASED ROUNDING
A mode is available on the ADSP-2181/ADSP-2183 to allow
biased rounding in addition to the normal unbiased rounding.
When the BIASRND bit is set to 0, the normal unbiased round-
ing operations occur. When the BIASRND bit is set to 1, biased
rounding occurs instead of the normal unbiased rounding.
When operating in biased rounding mode all rounding opera-
tions with MR0 set to 0x8000 will round up, rather than only
rounding odd MR1 values up. For example:
MR value before RND biased RND result unbiased RND result
00-0000-8000 00-0001-8000 00-0000-8000
00-0001-8000 00-0002-8000 00-0002-8000
00-0000-8001 00-0001-8001 00-0001-8001
00-0001-8001 00-0002-8001 00-0002-8001
00-0000-7FFF 00-0000-7FFF 00-0000-7FFF
00-0001-7FFF 00-0001-7FFF 00-0001-7FFF
This mode only has an effect when the MR0 register contains
0x8000; all other rounding operation work normally. This mode
allows more efficient implementation of bit-specified algorithms
that use biased rounding, for example the GSM speech com-
pression routines. Unbiased rounding is preferred for most
algorithms.
Note: BIASRND bit is bit 12 of the SPORT0 Autobuffer
Control register.
INSTRUCTION SET DESCRIPTION
The ADSP-2181/ADSP-2183 assembly language instruction set
has an algebraic syntax that was designed for ease of coding and
readability. The assembly language, which takes full advantage of
the processor’s unique architecture, offers the following ben-
efits:
• The algebraic syntax eliminates the need to remember cryptic
assembler mnemonics. For example, a typical arithmetic add
instruction, such as AR = AX0 + AY0, resembles a simple
equation.
• Every instruction assembles into a single, 24-bit word that
can execute in a single instruction cycle.
• The syntax is a superset ADSP-2100 Family assembly lan-
guage and is completely source and object code compatible
with other family members. Programs may need to be relo-
cated to utilize on-chip memory and conform to the ADSP-
2181/ADSP-2183’s interrupt vector and reset vector map.
• Sixteen condition codes are available. For conditional jump,
call, return, or arithmetic instructions, the condition can be
checked and the operation executed in the same instruction
cycle.
• Multifunction instructions allow parallel execution of an
arithmetic instruction with up to two fetches or one write to
processor memory space during a single instruction cycle.
I/O Space Instructions
The instructions used to access the ADSP-2181/ADSP-2183’s
I/O memory space are as follows:
Syntax: IO(addr) = dreg
dreg = IO(addr);
where addr is an address value between 0 and 2047 and dreg is
any of the 16 data registers.
Examples: IO(23) = AR0;
AR1 = IO(17);
Description: The I/O space read and write instructions move
data between the data registers and the I/O
memory space.
DESIGNING AN EZ-ICE-COMPATIBLE SYSTEM
The ADSP-2181/ADSP-2183 has on-chip emulation support and
an ICE-Port, a special set of pins that interface to the EZ-ICE.
These features allow in-circuit emulation without replacing the
target system processor by using only a 14-pin connection from
the target system to the EZ-ICE. Target systems must have a
14-pin connector to accept the EZ-ICE’s in-circuit probe, a 14-
pin plug. See the ADSP-2100 Family EZ-Tools data sheet for com-
plete information on ICE products.
The ICE-Port interface consists of the following ADSP-2181/
ADSP-2183 pins:
EBR
EBG
ERESET
EMS
EINT
ECLK
ELIN
ELOUT
EE