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 The VLB bus is obsolete and should not be used for new systems.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The VESA Local bus is obsolete and should not be used for new designs, the expansion slot will not exist on newer computers.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.
| 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. |
|
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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