Cypress CY7C1429BV18, CY7C1423BV18, CY7C1424BV18, CY7C1422BV18 Application Example, Echo Clocks

CY7C1422BV18, CY7C1429BV18

CY7C1423BV18, CY7C1424BV18

Echo Clocks DLL

Echo clocks are provided on the DDR-II to simplify data capture on high-speed systems. Two echo clocks are generated by the DDR-II. CQ is referenced with respect to C and CQ is referenced with respect to C. These are free-running clocks and are synchronized to the output clock of the DDR-II. In the single clock mode, CQ is generated with respect to K and CQ is generated with respect to K. The timing for the echo clocks is shown in Switching Characteristics on page 23.

These chips use a Delay Lock Loop (DLL) that is designed to function between 120 MHz and the specified maximum clock frequency. During power up, when the DOFF is tied HIGH, the DLL is locked after 1024 cycles of stable clock. The DLL can also be reset by slowing or stopping the input clocks K and K for a minimum of 30 ns. However, it is not necessary to reset the DLL to lock it to the desired frequency. The DLL automatically locks 1024 clock cycles after a stable clock is presented. The DLL may be disabled by applying ground to the DOFF pin. When the DLL is turned off, the device behaves in DDR-I mode (with one cycle latency and a longer access time). For information refer to the application note AN5062, DLL Considerations in QDRII/DDRII/QDRII+/DDRII+.

Application Example

Figure 1 shows four DDR-II SIO used in an application.

Figure 1. Application Example

	DATA IN
	DATA OUT
	Address
	LD#
	R/W#
BUS	BWS#
MASTER	SRAM 1 Input CQ
(CPU	SRAM 1 Input CQ#
or	SRAM 4 Input CQ
	SRAM 4 Input CQ#
ASIC)
	Source K
	Source K#
	Delayed K
	Delayed K#

SRAM 1

ZQ

SRAM 4

ZQ

B

Q

R = 250Ohms

B

Q

Vt

CQ

CQ

W

W

D

LD R/W

B

CQ#

D

LD R/W

CQ#

S

S

R

A

LD R/W W

A

#

#

#

#

#

#

C

C#

K

K#

C

C#

K

K#

#

#

#

Vt

Vt

R

R

R = 50Ohms

Vt = VREF

R = 250Ohms

Document #: 001-07035 Rev. *D Page 9 of 30

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