
256Kx18, Sync LW, HSTL, rev 4.6
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August 20, 1998
CXK77B1840GB
SONY
4A/4/45A/45
4Mb Late Write HSTL High Speed Synchronous SRAM (256K x 18 Organization)
Description
Features
R-R Mode
t
KHKH
/ t
KHQV
4.0ns / 2.3ns
4.0ns / 2.3ns
4.0ns / 2.3ns
5.0ns / 2.5ns
R-L, R-FT Modes
t
KHKH
/ t
KHQV
4.8ns / 4.8ns
5.3ns / 5.3ns
5.3ns / 5.3ns
6.5ns / 6.5ns
**DC Mode**
t
KHKH
/ t
KHQV
4.0ns / 5.2ns
4.0ns / 5.2ns
4.5ns / 6.0ns
4.5ns / 6.5ns
Fast Cycle/Access Time
CXK77B1840
-4A
-4
-45A
-45
Note: Contact Sony Memory Marketing for availability of DC mode functionality.
4 synchronous modes of operation, selectable by mode pins:
Register-Register; Register-Latch; Register-Flow Thru; Dual Clock
Single +3.3V power supply: 3.3V
±
5%
Dedicated output supply voltage: V
DDQ
(1.5V typical)
Inputs and outputs are HSTL / extended HSTL compatible.
Differential clock input (K/K, C/C).
All inputs (except asynchronous G and ZZ) and outputs are registered on a single clock edge.
Byte Write capability.
Late Write scheme to eliminate one dead cycle from Read-to-Write transitions.
Self-timed write cycles.
Sleep (power down) mode.
JTAG boundary scan (subset of IEEE standard 1149.1).
119 pin (7x17) Plastic Ball Grid Array (PBGA) package.
The CXK77B1840 is a high speed BiCMOS synchronous static RAM with common I/O pins, organized as 262,144-words by
18-bits. This synchronous SRAM integrates input registers, high speed RAM, output registers/latches, and a one-deep write
buffer onto a single monolithic IC. Four different read protocols - Register-Register (R-R), Register-Latch (R-L), Register-Flow
Thru (R-FT), and Dual Clock (DC), and an enhanced write protocol - Late (Delayed) Write (LW), are supported, providing a
flexible, high-performance user interface.
All input signals except G (Output Enable) and ZZ (Sleep Mode) are registered on the positive edge of K clock.
Read cycles can be controlled in one of four ways - with registered outputs in Register-Register mode, with latched outputs in
Register-Latch mode, with flow-through outputs in Register-Flow Thru mode, or with registered outputs using a dedicated out-
put control clock (C clock) in Dual Clock mode. The read protocol is user-selectable through external mode pins M1 and M2.
Write cycles follow a Late Write protocol, where data is provided to the SRAM one clock cycle after the address and control
signals, eliminating one dead cycle from Read-to-Write transitions. In this scheme, when a write cycle is initiated, the address
and data stored in the SRAM’s write buffer during the previous write cycle are directed to the SRAM’s memory core, while,
simultaneously, the address and data from the current write cycle are stored in the SRAM’s write buffer. In both Register-Latch
and Register-Flow Thru modes, when SW (Global Write Enable) is driven active, the subsequent positive edge of K clock tri-
states the SRAM’s output drivers immediately, allowing consecutive Read-Write-Read operations. The write cycle is internally
self-timed, which eliminates complex off-chip write pulse generation and provides increased flexibility for incoming signals.
The output drivers are series terminated, and the output impedance is programmable through an external impedance matching
resistor RQ. By connecting RQ between ZQ and V
SS
, the output impedance of all 18 DQ pins can be precisely controlled.
Sleep (power down) mode control is provided through the asynchronous ZZ input. 250 MHz operation is obtained from a single
3.3V power supply. JTAG boundary scan interface is provided using a subset of IEEE standard 1149.1 protocol.