1 Jan
2007
1 Jan
'07
2:16 p.m.
On 1 Jan 2007 at 10:47, dwight elvey wrote:
OK, I'll bite. What were the two instructions?
Most DSP's
are built around a MAC. I would guess the large word length
might be to include immediate coefficients.
Well, the 7720 has 3 or 4 instructions according to the manual (I
don't know who wrote it, but it's very confusing) which seems not to
be able to make up its mind.
Storage is a 23-bit instruction ROM, a 16-bit data ROM and a 16-bit
data RAM. Architecture is basically 1-address, with two selectable
accumulators.
Instruction I/II, OP and RT: Same format, but the RT also performs a
subroutine return at the conclusion. Fields designate ALU function,
source, destination, and address register modification. Instruction
is single-cycle.
Instruction III, JP: Jump; does conditional, unconditional jumps and
subroutine call.
Instruction IV, LD: Immediate load of value to selected
destination.
Now, I'd say that saying that there are only 3 instructions is sort
of cheating, but then, I didn't write the manual.
NEC doesn't call this chip a DSP; but an SPI (signal processing
interface). But it has the DSP earmark of compute-and-accumulate
capability with a 16x16 single-cycle multiplier.
Literature seems to date the chip sometime in 1983. Unfortunately, I
don't have one of the chips.
Cheers,
Chuck