In a neural network unit, each neural processing unit (NPU) of an array of N NPUs receives respective first and second upper and lower bytes of 2N bytes received from first and second RAMs. In a first mode, each NPU sign-extends the first upper byte to form a first 16-bit word and performs an arithmetic operation on the first 16-bit word and a second 16-bit word formed by the second upper and lower bytes. In a second mode, each NPU sign-extends the first lower byte to form a third 16-bit word and performs the arithmetic operation on the third 16-bit word and the second 16-bit word formed by the second upper and lower bytes. In a third mode, each NPU performs the arithmetic operation on a fourth 16-bit word formed by the first upper and lower bytes and the second 16-bit word formed by the second upper and lower bytes.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A neural network unit, comprising: first and second random access memories (RAM); an array of N neural processing units (NPU) configured to concurrently receive 2N bytes from a row of the first RAM and receive 2N bytes from a row of the second RAM, each NPU of the array receives respective first upper and lower bytes of the 2N bytes received from the first RAM and receives respective second upper and lower bytes of the 2N bytes received from the second RAM; when in a first mode, each NPU of the array sign extends the first upper byte to form a first 16-bit word and performs an arithmetic operation on the first 16-bit word and a second 16-bit word formed by the second upper and lower bytes; when in a second mode, each NPU of the array sign extends the first lower byte to form a third 16-bit word and performs the arithmetic operation on the third 16-bit word and the second 16-bit word formed by the second upper and lower bytes; and when in a third mode, each NPU of the array performs the arithmetic operation on a fourth 16-bit word formed by the first upper and lower bytes and the second 16-bit word formed by the second upper and lower bytes. 2. The neural network unit of claim 1, further comprising: each NPU of the array includes an accumulator that holds an accumulated value; and the arithmetic operation comprises a multiplication that generates a product and an accumulation of the product with the accumulated value that generates a sum to write into the accumulator. 3. The neural network unit of claim 2, further comprising: each NPU of the array includes two muxed-registers that receive the respective first upper and lower bytes from the first RAM to form a respective 16-bit word; and each of the two muxed-registers is coupled to rotate the formed respective 16-bit word to the two muxed-registers of an adjacent NPU of the array. 4. The neural network unit of claim 3, each NPU of the array is configured to: (a) receive the respective first upper and lower bytes from the row of the first RAM according to a first instance; (b) receive the respective second upper and lower bytes from the row of the second RAM to form a 16-bit word; (c) perform the multiplication and accumulation operations according to the first mode; (d) rotate the formed respective 16-bit word to the adjacent NPU of the array; (e) receive respective second upper and lower bytes from a successive row of the second RAM to form a 16-bit word; (f) perform the multiplication and accumulation operations according to the first mode; (g) repeat (d), (e) and (f) for each of M successive instances, where M is greater than two; (h) receive the respective first upper and lower bytes from the row of the first RAM according to a second instance; (i) receive respective second upper and lower bytes from a successive row of the second RAM to form a 16-bit word; (j) perform the multiplication and accumulation operations according to the second mode; (k) rotate the formed respective 16-bit word to the adjacent NPU of the array; (l) receive respective second upper and lower bytes from a successive row of the second RAM to form a 16-bit word; (m) perform the multiplication and accumulation operations according to the second mode; and (n) repeat (k), (1) and (m) for each of M successive instances. 5. The neural network unit of claim 1, further comprising: when in the first, second, and third modes, each NPU of the array generates a respective 16-bit result of the arithmetic operation performed. 6. The neural network unit of claim 5, further comprising: the neural network unit is further configured to write the N respective 16-bit results to a row of the first or second RAM. 7. The neural network unit of claim 6, further comprising: the neural network unit is further configured to perform an activation function on each of the N respective 16-bit results to generate N respective second results for writing to a row of the first or second RAM. 8. The neural network unit of claim 1, further comprising: when in a fourth mode, each NPU of the array sign extends the second upper byte to form a fifth 16-bit word and performs the arithmetic operation on the fifth 16-bit word and a sixth 16-bit word formed by the first upper and lower bytes; when in a fifth mode, each NPU of the array sign extends the second lower byte to form a seventh 16-bit word and performs the arithmetic operation on the seventh 16-bit word and the sixth 16-bit word formed by the first upper and lower bytes. 9. The neural network unit of claim 1, further comprising: when in a fourth mode, each NPU of the array performs an arithmetic operation on the first upper byte and the second upper byte and performs an arithmetic operation on the first lower byte and the second lower byte. 10. The neural network unit of claim 1, further comprising: the second RAM includes at least twice as many rows of 2N bytes as the first RAM. 11. The neural network unit of claim 1, further comprising: a program memory for holding instructions executable by the neural network unit. 12. A method for operating a neural network unit comprising first and second random access memories (RAM) and an array of N neural processing units (NPU) configured to concurrently receive 2N bytes from a row of the first RAM and receive 2N bytes from a row of the second RAM, each NPU of the array receives respective first upper and lower bytes of the 2N bytes received from the first RAM and receives respective second upper and lower bytes of the 2N bytes received from the second RAM, the method comprising: when in a first mode, sign-extending, by each NPU of the array, the first upper byte to form a first 16-bit word and performing an arithmetic operation on the first 16-bit word and a second 16-bit word formed by the second upper and lower bytes; when in a second mode, sign-extending, by each NPU of the array, the first lower byte to form a third 16-bit word and performing the arithmetic operation on the third 16-bit word and the second 16-bit word formed by the second upper and lower bytes; and when in a third mode, performing, by each NPU of the array, the arithmetic operation on a fourth 16-bit word formed by the first upper and lower bytes and the second 16-bit word formed by the second upper and lower bytes. 13. The method of claim 12, wherein each NPU of the array includes an accumulator that holds an accumulated value; and wherein the arithmetic operation comprises a multiplication that generates a product and an accumulation of the product with the accumulated value that generates a sum to write into the accumulator. 14. The method of claim 13, wherein each NPU of the array includes two muxed-registers that receive the respective first upper and lower bytes from the first RAM to form a respective 16-bit word; and wherein each of the two muxed-registers is coupled to rotate the formed respective 16-bit word to the two muxed-registers of an adjacent NPU of the array. 15. The method of claim 14, further comprising, by each NPU of the array: (a) receiving the respective first upper and lower bytes from the row of the first RAM according to a first instance; (b) receiving the respective second upper and lower bytes from the row of the second RAM to form a 16-bit word; (c) performing the multiplication and accumulation operations according to the first mode; (d) rotating the formed respective 16-bit word to the adjacent NPU of the array; (e) receiving respective second upper and lower bytes from a successive row of the second RAM to form a 16-bit word; (f) performing the multiplication and accumulation operations according to the first mode; (g) repeating (d), (e) and (f) for each of M successive instances, where M is greater than two; (h) receiving the respective first upper and lower bytes from the row of the first RAM according to a second instance; (i) receiving respective second upper and lower bytes from a successive row of the second RAM to form a 16-bit word; (j) performing the multiplication and accumulation operations according to the second mode; (k) rotating the formed respective 16-bit word to the adjacent NPU of the array; (l) receiving respective second upper and lower bytes from a successive row of the second RAM to form a 16-bit word; (m) performing the multiplication and accumulation operations according to the second mode; and (n) repeating (k), (1) and (m) for each of M successive instances. 16. The method of claim 12, further comprising: when in the first, second, and third modes, generating, by each NPU of the array, a respective 16-bit result of the arithmetic operation performed. 17. The method of claim 16, further comprising: writing the N respective 16-bit results to a row of the first or second RAM. 18. The method of claim 17, further comprising: performing an activation function on each of the N respective 16-bit results to generate N respective second results for writing to a row of the first or second RAM. 19. The method of claim 12, further comprising: when in a fourth mode, sign-extending, by each NPU of the array, the second upper byte to form a fifth 16-bit word and performing the arithmetic operation on the fifth 16-bit word and a sixth 16-bit word formed by the first upper and lower bytes; when in a fifth mode, sign-extending, by each NPU of the array, the second lower byte to form a seventh 16-bit word and performing the arithmetic operation on the seventh 16-bit word and the sixth 16-bit word formed by the first upper and lower bytes. 20. The method of claim 12, further comprising: when in a fourth mode, performing, by each NPU of the array, an arithmetic operation on the first upper byte and the second upper byte and performs an arithmetic operation on the first lower byte and the second lower byte. 21. A computer program product encoded in at least one non-transitory computer usable medium for use with a computing device, the computer program product comprising: computer usable program code embodied in said medium, for specifying a neural network unit, the computer usable program code comprising: first program code for specifying first and second random access memories (RAM); and second program code for specifying an array of N neural processing units (NPU) configured to concurrently receive 2N bytes from a row of the first RAM and receive 2N bytes from a row of the second RAM, each NPU of the array receives respective first upper and lower bytes of the 2N bytes received from the first RAM and receives respective second upper and lower bytes of the 2N bytes received from the second RAM; when in a first mode, each NPU of the array sign extends the first upper byte to form a first 16-bit word and performs an arithmetic operation on the first 16-bit word and a second 16-bit word formed by the second upper and lower bytes; when in a second mode, each NPU of the array sign extends the first lower byte to form a third 16-bit word and performs the arithmetic operation on the third 16-bit word and the second 16-bit word formed by the second upper and lower bytes; and when in a third mode, each NPU of the array performs the arithmetic operation on a fourth 16-bit word formed by the first upper and lower bytes and the second 16-bit word formed by the second upper and lower bytes.