The Board size and Pinout 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 The VLB bus is obsolete and should not be used for new systems.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 may be connected to the bus. Best speed is seen in the
Burst mode: Single address followed by 4 data transfers. 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
bit of data onto the address bus, producing a 64 bit data bus. The
reversion 2 VLB card is backward compatible with version 1. Because this
bus used the same bus structure as the 486, it could only be used with
the 486 class of processors, with the advent of the
Intel Pentium and the PCI bus - the VLB bus is now obsolete. The
pinout table provides row A which resides on the component side of the PC
board, while row B resides on the solder side. The VESA Local bus is
obsolete and should not be used for new designs. However, VESA Local Bus
board may be found in legacy equipment.
| 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. An 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. |
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Back to the main PC AT Bus page, or list of Personal Computer Buses
Design Key words for this page: PC, Personal Computer, VLB, VL-Bus, VESA Local Bus, PCAT, PCXT, ISA, PCI, Industry Standard Architecture Bus, Extended Industry Standard Architecture, Pinout, P2/J2 Pinouts, P1/J1 Pin out, J1 (A/B), J2 (C/D), Pin Outs, Connector, Signal Names, Pin descriptions, Card size, PWB Board Mechanical Dimensions, Mechanics Description, Electrical Interface, Parallel Bus, Physical Interface, Obsolete, Legacy, Out-dated, Expansion Bus, PC Board, Daughter Board, PC Card. |
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