WEBVTT 00:13.690 --> 00:19.630 Welcome to the unsigned and signed data types lecture and this lecture I'm going to explain VHDL unsigned 00:19.710 --> 00:27.160 and signed data types what is an unsigned data type and unsigned type is declared in the package numeric 00:27.160 --> 00:34.600 standard and one unsigned data type is there's an array of standard logic which we know a standard logic 00:34.690 --> 00:41.710 is an individual one or a zero a specific bit and a type unsigned is interpreted as a standard logic 00:41.710 --> 00:45.050 vector where we have a group of standard logic. 00:45.190 --> 00:50.440 But the difference is we have different operators available with a of logic vector we have. 00:50.440 --> 00:57.580 We can actually do addition or subtraction Hovell with the unsigned data type we can if we have to unsigned 00:57.690 --> 01:01.970 data types we can take and subtract them or add them to each other. 01:02.170 --> 01:06.910 And also we can manipulate the individual bits which is a major advantage. 01:06.910 --> 01:09.040 We can only with an unsigned type. 01:09.030 --> 01:11.590 We can only represent positive numbers. 01:11.590 --> 01:13.540 We can't represent a negative number. 01:13.660 --> 01:19.580 So once we get down to zero if we subtract one will still say zero we can't go to a negative one. 01:19.760 --> 01:28.240 And in the unsigned data type the leftmost bit is the NSB or the most significant bit. 01:28.270 --> 01:31.460 Let's take a look at an unsigned data type example. 01:31.480 --> 01:38.040 We have the data class which is a signal we have the signal name which is count. 01:38.050 --> 01:45.830 Then we have the colon and the data type which in this case is unsigned and HDL is denoted by just unsigned 01:46.480 --> 01:49.640 and we have the size of the unsigned data type. 01:49.780 --> 01:53.630 So here we have a data with minus one down to zero. 01:53.740 --> 02:00.490 So whenever either data with this if our data is a size of 8 we would take 8 minus one so B 7 down to 02:00.490 --> 02:05.150 zero which would give us a total of 8 bits in our unsigned data type. 02:05.440 --> 02:07.440 And then we have our. 02:07.750 --> 02:13.540 So my coin equals to give us our initial value which we have the other is keyword telling us that all 02:13.540 --> 02:17.960 these bits are set to zero no matter what size. 02:17.980 --> 02:23.740 For example if we want to have a signal a with an unsigned data type we'll make it three down to zero 02:23.800 --> 02:29.860 which gives us 4 bits wide and we want to set that value to 13 which would be the binary value of 1 02:29.860 --> 02:35.860 1 0 1 with your leftmost bit being less inefficient that we Abdus up. 02:35.860 --> 02:37.970 That gives a value of 13. 02:38.440 --> 02:40.930 And if we take another signal we'll call signal B. 02:41.000 --> 02:47.780 I give it an unsigned data type with 3 down to zero which also is an 0 4 bits of one set that night 02:47.780 --> 02:53.350 of 5 and 0 1 0 1 leftmost bit is the most significant bit. 02:53.410 --> 03:01.860 And so that is how you would set the initial value of b to 5 now talk about our signed data types these 03:01.950 --> 03:03.480 are also declared in the package. 03:03.510 --> 03:10.110 Numeric standard just like the unsigned data types are and as well these are an array of stand who logic 03:10.410 --> 03:11.940 just like the unsigned data type. 03:11.940 --> 03:19.860 However the difference between the unsigned versus the signed is that you're signed data types can represent 03:19.920 --> 03:21.400 negative numbers. 03:21.540 --> 03:24.990 And the way they're stored are in twos complement form. 03:25.020 --> 03:30.660 So if you want to represent a negative five depending on the number of bits you specified for your data 03:30.660 --> 03:37.200 type you'll want to take negative five and the two's complement form and store it inside in the leftmost 03:37.200 --> 03:42.790 bit just like the unsigned data type is the MSP or the most significant bit. 03:42.830 --> 03:47.510 Well let's take a look at what a signed data type example looks like. 03:47.610 --> 03:50.460 We have our data class which is a signal. 03:50.490 --> 03:58.170 We have our signal name calling count and data type we're specifying assigned and then the size of that 03:58.170 --> 03:59.040 sign data type. 03:59.040 --> 04:01.580 How many bits is that signed data type. 04:01.680 --> 04:05.450 In this case we're saying data wit minus one down to zero. 04:05.490 --> 04:13.110 So our data with this if we have 8 bits we subtract one gives a 7 down to zero which are give us 8 bit 04:13.110 --> 04:19.100 number for Assigned data type and then the initial value which we are specifying them all to be zeros 04:19.950 --> 04:23.560 which is what the others keyword specifies. 04:23.610 --> 04:29.600 So let's say we have a signal a which is assigned to type signal we'll call it from 3 down to zero. 04:29.610 --> 04:34.910 So that gives us four bits and we want to have a negative three value. 04:35.070 --> 04:37.230 So we have to store this in twos complement. 04:37.440 --> 04:40.500 So that's where we have a 1 1 0 1. 04:40.500 --> 04:43.930 The leftmost bit is used to signify that it's negative. 04:44.070 --> 04:47.760 So we know that's a negative 3 and two's complement form. 04:47.760 --> 04:50.270 Now we want to have a positive five. 04:50.340 --> 04:53.950 We have our signal B which is assigned to type as well. 04:53.970 --> 05:01.650 Three down to zero gives us our four bits and we would specify or initial value is 0 1 0 1 and that's 05:01.650 --> 05:05.280 how you would set assign data type to a value of 5. 05:06.540 --> 05:09.290 And that is the signed unsigned datatypes lecture.