Datasheet
SN74VMEH22501A
SCES3620A –DECEMBER 2004–REVISED FEBRUARY 2010
www.ti.com
FUNCTIONAL DESCRIPTION
The SN74VMEH22501A is a high-drive (–48/64 mA), 8-bit UBT transceiver containing D-type latches and D-type
flip-flops for data-path operation in transparent, latched, or flip-flop modes. Data transmission is true logic. The
device is uniquely partitioned as 8-bit UBT transceivers with two integrated 1-bit three-wire bus transceivers.
Functional Description for Two 1-Bit Bus Transceivers
The OEAB inputs control the activity of the 1B or 2B port. When OEAB is high, the B-port outputs are active.
When OEAB is low, the B-port outputs are disabled.
Separate 1A and 2A inputs and 1Y and 2Y outputs provide a feedback path for control and diagnostics
monitoring. The OEBY inputs control the 1Y or 2Y outputs. When OEBY is low, the Y outputs are active. When
OEBY is high, the Y outputs are disabled.
The OEBY and OEAB inputs can be tied together to form a simple direction control where an input high yields
A data to B bus and an input low yields B data to Y bus.
1-BIT BUS TRANSCEIVER FUNCTION TABLE
INPUTS
OUTPUT MODE
OEAB OEBY
L H Z Isolation
H H A data to B bus
True driver
L L B data to Y bus
H L A data to B bus, B data to Y bus True driver with feedback path
Functional Description for 8-Bit UBT Transceiver
The 3A and 3B data flow in each direction is controlled by the OE and direction-control (DIR) inputs. When OE is
low, all 3A- or 3B-port outputs are active. When OE is high, all 3A- or 3B-port outputs are in the high-impedance
state.
FUNCTION TABLE
INPUTS
OUTPUT
OE DIR
H X Z
L H 3A data to 3B bus
L L 3B data to 3A bus
The UBT transceiver functions are controlled by latch-enable (LE) and clock (CLKAB and CLKBA) inputs. For
3A-to-3B data flow, the UBT operates in the transparent mode when LE is high. When LE is low, the 3A data is
latched if CLKAB is held at a high or low logic level. If LE is low, the 3A data is stored in the latch/flip-flop on the
low-to-high transition of CLKAB.
The UBT transceiver data flow for 3B to 3A is similar to that of 3A to 3B, but uses CLKBA.
4 Submit Documentation Feedback Copyright © 2004–2010, Texas Instruments Incorporated
Product Folder Link(s): SN74VMEH22501A