Data transfer system for a data processing system provided with direct memory access units
First Claim
1. In a data processing system which includes a central processing unit with an n-bit word length, where n is a positive integer having a value greater than 7, a main memory, a plurality of direct memory access units and an n-bit data bus coupling the central processing unit, the main memory and the direct memory access units for transfer of data between the direct memory access units and the main memory, the improvement comprising a data transfer system for accessing the main memory, the data transfer system comprising:
- (a) said main memory being capable of storing n-bit full-words in byte units, each full-word made up of m bytes where n/m is the number of bits in one byte and said memory having a separate transfer enable input for each of said m bytes;
(b) said direct memory access units comprising at least one first direct memory access unit which can receive and deliver n-bit full-words, and at least one second direct memory access unit which can receive and deliver n/2 bit half-words, since n/2 is an integer;
(c) a plurality of gate circuits coupling the main memory and the data bus line;
(d) first data transfer control means for controlling the gate circuits so that data transfer is achieved between the main memory and the first direct memory access unit, using n bits of the data bus line and an n-bit memory location when the first direct memory access unit has access to the main memory;
(e) zone specifying means having m zone selection inputs from the Central Processing unit, one corresponding to each of said m bytes in said main memory and responsive to said zone selection inputs and a control output from said first data transfer control means indicative of data transfer between the main memory and the first direct memory access unit, for selectively providing at least one signal to said separate transfer enable inputs to enable, transfer of at least one byte of data between an n-bit memory location and said first direct memory access unit using a corresponding part of the n-bit data bus line and the first direct memory access unit whereby through use of said zone specifying means appropriate zones within an n-bit full-word or a half-word may be specified; and
(f) second data transfer control means for controlling the gate circuits so that data transfer is achieved between the main memory and the second direct memory access unit, using n/2 bits of the data bus line and n/2 bits from an n bit memory location when the second direct memory access unit has access to the main memory.
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Abstract
A data transfer system is disclosed which includes a main memory, a memory control unit for controlling the operation of the main memory, a central processing unit, a plurality of direct memory access units each provided with at least two data transfer bus widths, a common data bus line, and a common memory address/control line. A control line is provided for distinguishing between the at least two data transfer bus widths and is only connected between a direct memory access unit provided with the memory control unit, the central processing unit and one of the at least two data transfer bus widths. When data is transferred, using one of the data transfer bus widths, the control line is energized with a control signal which is delivered to the memory control unit. On the other hand, the direct memory access unit which has the other data transfer bus width is not connected to the control line thereby preventing it from becoming energized.
The memory control unit controls the operation of a gate circuit between the memory data line which is connected between the main memory and the data bus line and the read data line and generates a write enable signal for effecting a writing of data in byte units in either an even number address or an odd number address thereof.
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Citations
6 Claims
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1. In a data processing system which includes a central processing unit with an n-bit word length, where n is a positive integer having a value greater than 7, a main memory, a plurality of direct memory access units and an n-bit data bus coupling the central processing unit, the main memory and the direct memory access units for transfer of data between the direct memory access units and the main memory, the improvement comprising a data transfer system for accessing the main memory, the data transfer system comprising:
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(a) said main memory being capable of storing n-bit full-words in byte units, each full-word made up of m bytes where n/m is the number of bits in one byte and said memory having a separate transfer enable input for each of said m bytes; (b) said direct memory access units comprising at least one first direct memory access unit which can receive and deliver n-bit full-words, and at least one second direct memory access unit which can receive and deliver n/2 bit half-words, since n/2 is an integer; (c) a plurality of gate circuits coupling the main memory and the data bus line; (d) first data transfer control means for controlling the gate circuits so that data transfer is achieved between the main memory and the first direct memory access unit, using n bits of the data bus line and an n-bit memory location when the first direct memory access unit has access to the main memory; (e) zone specifying means having m zone selection inputs from the Central Processing unit, one corresponding to each of said m bytes in said main memory and responsive to said zone selection inputs and a control output from said first data transfer control means indicative of data transfer between the main memory and the first direct memory access unit, for selectively providing at least one signal to said separate transfer enable inputs to enable, transfer of at least one byte of data between an n-bit memory location and said first direct memory access unit using a corresponding part of the n-bit data bus line and the first direct memory access unit whereby through use of said zone specifying means appropriate zones within an n-bit full-word or a half-word may be specified; and (f) second data transfer control means for controlling the gate circuits so that data transfer is achieved between the main memory and the second direct memory access unit, using n/2 bits of the data bus line and n/2 bits from an n bit memory location when the second direct memory access unit has access to the main memory. - View Dependent Claims (2, 3, 4, 5, 6)
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Specification