LF3312 Datasheet, PDF (8/33 Pages) LOGIC Devices Incorporated – 12-Mbit Frame Buffer / FIFO

DEVICES INCORPORATED
LF3312
12-Mbit Frame Buffer / FIFO
Preliminary Datasheet
Cascading Devices for Depth Expansion
Multiple devices can be cascaded to deepen the address space. The usable 24bit address space is simply
extended for every additional device that is cascaded.
Internally, the LF3312 has a 24bit address space. When cascading LF3312s, each device’s write and read
pointers behave identically. The LF3312 was designed to be cascaded in parallel. That is, the inputs of each
device are tied together. The input data word (the data word placed on the AIN input port) is to be common
for all devices. Similarly, the outputs of all devices are tied together. Only one device drives the shared
output bus at one time, controlled automatically through internal bus enables.
Each device in a cascade of N devices is responsible for 1/N of the address space. That is, each device
writes and/or reads based on the common W/R pointer locations and where that particular device sits in
the cascade. Configuration Register C[3:0] (BASE_ADDR) is used to define each device’s place in the
cascade.
When cascading LF3312s, only singe-channel modes are supported (OPMODES 0 to 3). All write enables
AWEN/BWEN and AIEN/BIEN must be tied together, as must read enables AREN/BREN (see the device
connection diagram below).
The configuration registers of each device must be programmed identically, depending on mode/function,
except for Register C. Register C defines which region of the 24bit address space the particular device is
responsible for. Within Register C, there is a 4bit BASE_ADDR and 4bit CASCADE word. BASE_ADDR
determines the region of address space each device controls, and CASCADE defines how many devices
are in cascade. Register C effectively is programmed as “Chip n of N”.
Figure 4. 24Mbit FIFO Depth Expansion: Two Cascaded Devices
WCLK
ASET
BSET
ACLR
BCLR
WEN
IEN
AIN11-0 ¹²
LF3312_1
AWCLK
BWCLK
ASET
BSET
ACLR
BCLR
AWEN
BWEN
AIEN
BIEN
RCLK
AREN
BREN
RSET
RCLR
AIN
AOUT
RCLK
REN
RSET
RCLR
12
AOUT11-0
12
ADDR11-0
BIN
BOUT
12
ADDR23-12
LF3312_2
AWCLK
BWCLK
ASET
BSET
ACLR
BCLR
AWEN
BWEN
AIEN
BIEN
RCLK
AREN
BREN
RSET
RCLR
AIN
AOUT
BIN
BOUT
LOGIC Devices Incorporated
Video Imaging Product
8
August 8, 2006 LDS.3312 O