6.42

IDT7133SA/LA, IDT7143SA/LA

High-Speed 2K x 16 Dual-Port RAM

Military, Industrial and Commercial Temperature Ranges

14

Functional Description

The IDT7133/43 provides two ports with separate control, address

and I/O pins that permit independent access for reads or writes to any

location in memory. The IDT7133/43 has an automatic power down

feature controlled by

CE. The CE controls on-chip power down circuitry

that permits the respective port to go into a standby mode when not

selected (

CE HIGH). When a port is enabled, access to the entire

memory array is permitted. Non-contention READ/WRITE conditions

are illustrated in Truth Table 1.

Busy Logic

Busy Logic provides a hardware indication that both ports of the

RAM have accessed the same location at the same time. It also allows

one of the two accesses to proceed and signals the other side that the

RAM is “busy”. The

BUSY pin can then be used to stall the access until

the operation on the other side is completed. If a write operation has

been attempted from the side that receives a

BUSY indication, the

write signal is gated internally to prevent the write from proceeding.

The use of

BUSY logic is not required or desirable for all applica-

tions. In some cases it may be useful to logically OR the

BUSY outputs

together and use any

BUSY indication as an interrupt source to flag the

event of an illegal or illogical operation. If the write inhibit function of

BUSY logic is not desirable, the

BUSY logic can be disabled by using

the IDT7143 (SLAVE). In the IDT7143, the

BUSY pin operates solely

as a write inhibit input pin. Normal operation can be programmed by

tying the

BUSY pins HIGH. If desired, unintended write operations can

be prevented to a port by tying the

BUSY pin for that port LOW. The

BUSY outputs on the IDT 7133 RAM are open drain and require pull-

up resistors.

Width Expansion with Busy Logic

Master/Slave Arrays

When expanding an IDT7133/43 RAM array in width while using

BUSY logic, one master part is used to decide which side of the RAM

array will receive a

BUSY indication, and to output that indication. Any

number of slaves to be addressed in the same address range as the

master, use the

BUSY signal as a write inhibit signal. Thus on the

IDT7133 RAM the

BUSY pin is an output and on the IDT7143 RAM, the

BUSY pin is an input (see Figure 3).

Expanding the data bus width to 32 bits or more in a Dual-Port RAM

system implies that several chips will be active at the same time. If each

chip includes a hardware arbitrator, and the addresses for each chip

arrive at the same time, it is possible that one will activate its

while another activates its

and the CPUs will await indefinitely for their port to become free.

To avoid the “Busy Lock-Out” problem, IDT has developed a

MASTER/SLAVE approach where only one hardware arbitrator, in the

MASTER, is used. The SLAVE has

BUSY inputs which allow an

interface to the MASTER with no external components and with a

speed advantage over other systems.

When expanding Dual-Port RAMs in width, the writing of the SLAVE

RAMs must be delayed until after the

BUSY input has settled.

Otherwise, the SLAVE chip may begin a write cycle during a contention

situation. Conversely, the write pulse must extend a hold time past

BUSY to ensure that a write cycle takes place after the contention is

resolved. This timing is inherent in all Dual-Port memory systems where

more than one chip is active at the same time.

The write pulse to the SLAVE should be delayed by the maximum

arbitration time of the MASTER. If, then, a contention occurs, the write

to the SLAVE will be inhibited due to

BUSY from the MASTER.

Figure 4. Busy and chip enable routing for both width and depth expansion

with the IDT7133 (MASTER) and the IDT7143 (SLAVE).

R/

W

BUSY

R/

W

BUSY

IDT7133

MASTER

R/

W

BUSY

R/

W

BUSY

R/

W

BUSY

R/

W

BUSY

LEFT

RIGHT

2746 drw 15

IDT7143

SLAVE

270

Ω

270

Ω