Browse Prior Art Database

Data Latching Technique

IP.com Disclosure Number: IPCOM000101045D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Wroe, KE: AUTHOR [+3]

Abstract

Described is a system of latching serial data from VRAMs (Video Random- Access Memories) without requiring an extra clock pulse to latch the final data. The time window during which latched data is valid is maximized, giving the advantages of both edge-triggered and transparent latches.

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Data Latching Technique

       Described is a system of latching serial data from VRAMs
(Video Random- Access Memories) without requiring an extra clock
pulse to latch the final data.  The time window during which latched
data is valid is maximized, giving the advantages of both
edge-triggered and transparent latches.

      Referring to Fig. 1, data is clocked from the serial port of a
VRAM in a read cycle by the rising edge of the serial clock.  When
the serial port is clocked at its maximum rate, the serial data may
be ideally latched externally using the rising edge of the following
serial clock.  With a D-type edge-triggered system, the serial clock
could be used to clock the external latches directly, and the latch
outputs would have a valid data window of a full serial clock cycle
time.  However, an extra serial clock would be required at the end of
every burst, e.g., at the end of a video scan line, just to latch the
last necessary data.  This is illustrated in Fig. 2.  To provide an
extra serial clock at the end of a video scan line may cause extra
logic complexity for the memory controller and lengthen the minimum
achievable flyback time.

      This article describes an alternative system, using LSSD (Level
Sensitive Scan Design)-type transparent latches to avoid the need for
the extra serial clock.  The latches are clocked with an inverted
form of the VRAM serial clock. They are therefore open when the
serial clock is low, and close on the ri...