VESA Local Bus


VLB Expansion Slot

The board size and pin out for the VESA Local Bus [VLB] bus is shown below. The VLB bus is obsolete and should not be used for new systems.
However the pin out table may be used for legacy computer systems.
VESA [Video Electronic Standards Association] Local bus [VLB or VL-Bus] operated at 33MHz with a 16/32 data bits, and 30 address bits. The VLB was released in 1992 and operated as a PC Local Bus Expansion. A maximum of three devices could be connected to the bus. Best speed is seen in the Burst mode: Single address followed by 4 data transfers. The VLB interface supports bus mastering. The VLB resides on a standard 16-bit ISA card with the additional pins required by the VLB interface residing after the ISA pins, allowing an ISA card to use the same slot. Refer to this page for the ISA pinout. Revision 2 of VLB multiplexed 32 bits of data onto the address bus, producing a 64 bit data bus. A reversion 2 VLB card is backward compatible with version 1. Because this interface used the same bus structure as the 486, it could only be used with the 486 class of processors, so with the advent of the Intel Pentium and the PCI bus - the VLB bus became obsolete. The pinout table provides row A which resides on the component side of the PC board [top-side], while row B resides on the solder side [bottom-side].
The VESA Local bus is obsolete and should not be used for new designs, the expansion slot will not exist on newer computers.
However, the VESA Local Bus board, along with a local bus expansion slot might be found in legacy equipment, or older gear.





PC VLB Card Size

VL-Bus Board Size


PC VLB Connector Pinout
Pin Name Description Pin Name Description
A1 D1 Data 1 B1 D0 Data 0
A2 D3 Data 3 B2 D2 Data 2
A3 GND Ground B3 D4 Data 4
A4 D5 Data 5 B4 D6 Data 6
A5 D7 Data 7 B5 D8 Data 8
A6 D9 Data 9 B6 GND Ground
A7 D11 Data 11 B7 D10 Data 10
A8 D13 Data 13 B8 D12 Data 12
A9 D15 Data 15 B9 VCC +5 VDC
A10 GND Ground B10 D14 Data 14
A11 D17 Data 17 B11 D16 Data 16
A12 Vcc +5 VDC B12 D18 Data 18
A13 D19 Data 19 B13 D20 Data 20
A14 D21 Data 21 B14 GND Ground
A15 D23 Data 23 B15 D22 Data 22
A16 D25 Data 25 B16 D24 Data 24
A17 GND Ground B17 D26 Data 26
A18 D27 Data 27 B18 D28 Data 28
A19 D29 Data 2 B19 D30 Data 30
A20 D31 Data 31 B20 VCC +5 VDC
A21 A30 Address 30 B21 A31 Address 31
A22 A28 Address 28 B22 GND Ground
A23 A26 Address 26 B23 A29 Address 29
A24 GND Ground B24 A27 Address 27
A25 A24 Address 24 B25 A25 Address 25
A26 A22 Address 22 B26 A23 Address 23
A27 VCC +5 VDC B27 A21 Address 21
A28 A20 Address 20 B28 A19 Address 19
A29 A18 Address 18 B29 GND Ground
A30 A16 Address 16 B30 A17 Address 17
A31 A14 Address 14 B31 A15 Address 15
A32 A12 Address 12 B32 VCC +5 VDC
A33 A10 Address 10 B33 A13 Address 13
A34 A8 Address 8 B34 A11 Address 11
A35 GND Ground B35 A9 Address 9
A36 A6 Address 6 B36 A7 Address 7
A37 A4 Address 4 B37 A5 Address 5
A38 WBACK# Write Back B38 GND Ground
A39 BE0# Byte Enable 0 B39 A3 Address 3
A40 VCC +5 VDC B40 A2 Address 2
A41 BE1# Byte Enable 1 B41 n/c Not connected
A42 BE2# Byte Enable 2 B42 RESET# Reset
A43 GND Ground B43 DC# Data/Command
A44 BE3# Byte Enable 3 B44 M/IO# Memory/IO
A45 ADS# Address Strobe B45 W/R# Write/Read
-- Key No Pins -- Key No Pins
A48 LRDY# Local Ready B48 RDYRTN# Ready Return
A49 LDEV Local Device B49 GND Ground
A50 LREQ Local Request B50 IRQ9 Interrupt 9
A51 GND Ground B51 BRDY# Burst Ready
A52 LGNT Local Grant B52 BLAST# Burst Last
A53 VCC +5 VDC B53 ID0 Identification 0
A54 ID2 Identification 2 B54 ID1 Identification 1
A55 ID3 Identification 3 B55 GND Ground
A56 ID4 Identification 4 B56 LCLK Local Clock
A57 LKEN# Enable B57 VCC +5 VDC
A58 LEADS# Local Enable Address Strobe B58 LBS16# Local Bus Size 16




The PCXT bus pinout uses the J1 A/B rows, and a PCAT bus pin out uses the J1 [A/B rows] and J2 [C/D rows] connectors. The PC VLB pinout is shown after the XT and AT pins [see the PC-AT board page]. The ISA fingers are copper strips on the PWB spaced on 0.1 inch centers. The PCAT bus [ISA] was an up-grade to the original PCXT bus, and the VLB bus was an up-grade to the PC-AT bus. A ISA card will work in a VLB slot, but an VLB card will not work in an AT slot. The Pin out for the VLB bus type are shown in the table above. The connector positions and relationship to the board are shown in the figure at the top of the page. Example dimensions for the card size is provided. The Personal Computer Motherboard could then accept either an 8 or 16 bit card in an 8 bit slot (XT), or (if the connector was provided) a 16 bit card in an AT slot. A maximum number of 8 Expansion slots were provided on IBM compatible Mother boards.
Only three VLB boards could be used in a system, each board would use the same VL-Bus 'interface' reducing the speed for each card.

The VESA expansion slot is no longer found on modern personal computers.

Back to the main PC AT Bus page, or list of Personal Computer Buses.


Navigation: Engineering Home > Interface Buses > Personal Computer Buses > PC-AT Expansion Card > VESA Expansion Card.


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Modified 2/4/12
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