How do I find two's complement for hex F3A1?
First I converted the number to binary 1111 0011 1010 0001 and then I found two's complement 0000 1100 0101 1111 givin' as result 0C5F which differs from the answer in the book: 0A57
What I'm doing wrong?
Two’s complement of hexadecimal
digital-logic
Related Solutions
with input select
led <= table(to_integer(unsigned(d & tmp)))
when "0000" | "0001" | "0010" | "0011" |
"0100" | "0101" | "0110" | "0111" |
"1000" | "1001" | "1010" | "1011" |
"1100" | "1101" | "1110" | "1111"
and ob = '1',
...
The syntax error occurs at the "and" clause which is not part of a valid "select" choice list.
However note that the "when" expression is equivalent to ignoring the "input" altogether so
with ob select
led <= table(to_integer(unsigned(d & tmp))) when '1',
...
You may be under the misapprehension that explicitly specifying all combinations of '0' and '1' values for "input" excluded any input values containing 'X', 'U', '-' etc (of these symbols, only one is a "don't care").
Indeed in simulation it may actually work; however a little thought will show that there is no synthesisable hardware primitive that can reliably do so, and unless you are writing a testbench, this is certainly the wrong approach altogether and the simple syntax error is the least of your problems.
EDIT : here's one way (untested) using both a table and a selected signal assignment, using don't cares to reduce the table size. Some further simplification may be possible.
architecture myarch of pitch_decoder_2 is
type tbl is array (3 downto -4) of std_logic_vector(9 downto 0);
constant table : tbl := (
"0111100000", -- 3
"0011100000", -- 2
"0001100000", -- 1
"0000100000", -- 0
"0000110000", -- -1
"0000111000", -- -2
"0000111100", -- -3
"0000111110"); -- -4
signal sel : signed(3 downto 0);
begin
sel <= (d xor ob) & c & b & a;
with sel select led <=
"1111100000" when "01--",
table(to_integer(sel)) when "00--" | "11--",
"0000111111" when "10--",
"----------" when others;
end myarch;
The problem is that your bit inputs must be at either a logical 1 (Vcc) or a logical zero, (GND) as they would be if they were connected to the outputs of, say, a counter like an HC191.
You've shown them floating when the switch is OFF, which won't work properly if you're using an R-2R ladder.
This works, and here are the LTspice files so you can play with the circuit if you want to.
Best Answer
Flip 1's to 0's and 0's to 1's (i.e. regular complement). Then add 1.
What you're doing wrong is having too much faith in a book.
But, on the bright side, at least it's some kind of technical book that is probably mostly correct.