NuBus™ ADDRESS/DATA TRANSCEIVERS AND REGISTERS
• Designed for NuBus™ Interface
• Conforms to ANSI/IEEE Std 1196-1987
• On-Chip Comparator Provides I/D Slot
• Multiplexed Real-Time and Latched
• Designed to Operate With SN74ACT2440
• BiCMOS Design Substantially Reduces
• Dependable Texas instruments Quality and
The ’BCT2420 consists of bus transceiver circuits,
D-type flip-flops, latches, and control circuitry
arranged for multiplexed transmission of address
and data information in NuBus™ applications. An
on-chip comparator has been included to detect
when a NuBus™ transfer cycle is requesting the
local board. The device conforms to ANSI/IEEE
Std 1196-1987 and operates with Texas instru-
ments SN74ACT2440 NuBus™ Controller. In
addition, the device is easily configured around
ASIC or other PAL® -based controllers.
SDIS007A – D3159, NOVEMBER 1988 – REVISED JANUARY 1989
9 8 7 6 5 4 3 2 1 68 67 66 65 64 63 62 61
27 28 29 30 31 32 33 34 3536 37 38 39 40 41 42 43
The ’BCT2420 was designed using Texas Instruments BiCMOS process, which features bipolar drive
characteristics and greatly reduces the standby power of the device when disabled. This feature is especially
valuable when the device is not performing a NuBus™ transaction.
The AEN, DEN and ADEN inputs control the transceiver functions. Three 16-bit I/O ports, A15–A0, D15–D0,
and AD15–AD0, provide for address and data transfer. When the NuBus™ performs a write cycle to the local
board, address information is saved on the rising edge of ACLK. During the last portion of the NuBus™ write
cycle, data information is saved on the rising edge of DCLK.
When the local board is performing a write to the NuBus™, address and data is multiplexed onto the NuBus™
via the A/D line. Address and data can be latched by using the ALE and DLE input lines respectively.
The IDEQ output is used to signal that the local board is being requested by the NuBus™. This output is typically
fed to the NuBus™ controller. IDEQ goes active (low) when AD15–AD12 are low and AD11–AD8 match ID3–ID0.
IDEQ stays valid until the next address clock (ACLK) occurs. Internal 10-kΩ pullup resistors are included on the
The SSEQ output is used to signal the local board that super-slot addresses are being requested. This output
is active (low) whenever AD15–AD12 are equal to ID3–AD0, except when ID3–ID0 are all low.
In typical NuBus™ applications, two devices are required to provide the full 32-bit address/data path. Refer to
the typical NuBus™ interface diagram on page 9 for additional information.
The SN74BCT2420 is characterized for operation from 0°C to 70°C.
NuBus is a trademark of Texas Instruments Incorporated.
PAL is a registered trademark of Monolithic Memories Inc.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
•POST OFFICE BOX 655303 DALLAS, TEXAS 75265
Copyright © 1989, Texas Instruments Incorporated