Message FIFO buffer controller

• US 4,873,666 A
• Filed: 10/15/1987
• Issued: 10/10/1989
• Est. Priority Date: 10/14/1987
• Status: Expired due to Term

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: Northern Telecom Limited (Nortel Networks Corporation)
• Inventors: Ciancibello, Carmine A., Lefebvre, Martin C., Geadah, Youssef A.
• Primary Examiner(s): GOSSAGE, GLENN
• Application Number:
  US07/108,655
• Time in Patent Office: 726 Days
• Field of Search: 365/189, 365/221, 365/236, 365/239, 365/78, 365/230, 340/750, 340/799, 340/802, 340/800, 364/200 MS File, 364/900 MS File
• US Class Current: 365/189.07
• CPC Class Codes: G06F 2205/062 Allowing rewriting or rereading data to or from the buffer
• CPC Class Codes: G06F 5/14 for overflow or underflow handling, e.g. full or empty flags

Abstract

A FIFO (first in first out) control circuit for providing address information to a FIFO memory uses two up counters--one to provide the write address and one to provide the read address. A multiplexer selects which addresses (read or write) are used. Two storage registers are used to temporarily "hold" the output from the counters. This enables the counters to be re-loaded with their original "count" to enable either a re-reading or a re-writing of a message stored in the FIFO memory. Comparators and logic circuitry are used to provide two status output signals, namely full (or not) and empty (or not).

Claims

1. A control circuit for a FIFO (first in first out) memory circuit for providing address information to a FIFO memory means having an address field of n bits, said control circuit comprising:

a first means for providing a first binary signal having n+1 bits;

a second means for providing a second binary signal having n+1 bits;

a first storage means for selectively receiving and storing the output of said first means;

second storage means for selectively receiving and storing the output of said second means;

first comparator means for comparing the output of said first storage means with the output of said second means and producing a first control signal indicative of said comparison; and

second comparator means for comparing the output of said second storage means with the output of said first means and producing a second control signal indicative of said comparison.

2. The control circuit of claim 1 wherein said first means is a counter means and wherein said second means is a counter means.

3. The control circuit of claim 2 further including a multiplexer means for receiving both said first signal and said second signal and selecting either said first or said second signal as its output whereby the n least significant bits output from said multiplexer are used to address said FIFO memory.

4. The control circuit of claim 1, 2, or 3 wherein said second comparator comprises:

third comparator means for comparing the most significant bit of said first signal with the most significant bit of the output from said second storage means and producing a third control signal indicative of said comparison;

fourth comparator means for comparing the n least significant bits of said first signal with the n least significant bits from said second storage means and producing a fourth control signal indicative of said comparison;

logic means, responsive to said third control signal and said fourth control signal, to produce said second control signal indicative of said memory circuit being full or not full.

5. A control circuit for a FIFO (first in first out) memory circuit for producing address information to a FIFO memory means having an address field of n bits, said control device comprising:

first counter means for providing a first binary signal having n+1 bits;

second counter means for providing a second binary signal having n+1 bits;

multiplexer means for receiving both said first signal and said second signal and selecting either said first or second signal as its output;

first storage means for selectively receiving and storing the output of said first counter means;

second storage means for selectively receiving and storing the output of said second counter means;

first bus means for applying the output of sid first storage means to said first counter means;

second bus means for applying the output of said second storage means to said second counter means;

first comparator means for comparing the output of said first storage means with the output of said second counter means and producing a first control signal indicative of said comparison; and

second comparator means for comparing the output of said second storage means with the output of said first counter means and producing a second control signal indicative of said comparison;

whereby the n least significant bits output from said multiplexer are used to address said FIFO memory.

6. The control circuit of claim 5 wherein said first storage means is a binary storage register and wherein said second storage means is a binary storage register.

7. The control circuit of claim 6 wherein said second comparator comprises:

third comparator means for comparing the most significant bit of said first signal with the most significant bit of the output from said second storage means and producing a third control signal indicative of said comparison;

fourth comparator means for comparing the n least significant bits of said first signal with the n least significant bits from said second storage and producing a fourth control signal indicative of said comparison; and

logic means, responsive to said third control signal and said fourth control signal, to produce said second control signal indicative of said memory circuit being full or not full.

8. The control circuit of claim 7 wherein said logic means is an AND gate.