DOS Days

Cirrus Logic CL-GD5420 / CL-GD5421

The CL-GD5420 was an ISA Super VGA chipset released in 1992. Cards also got the label AVGA3 or AVGA3B, indicating it was a successor to Cirrus Logic's earlier AVGA and AVGA2. The chip was highly integrated with an embedded 15-bit RAMDAC and PLL. The CL-GD5421 was a minor upgrade over the 5420 with a 16-bit RAMDAC, also commonly referred to as High Color or "Hi-Color".

Released 1992
Bus ISA 16-bit
Chipset Cirrus Logic CL-GD5420 or CL-GD5421
Standards MDA, Hercules, CGA, EGA, VGA
Memory 256 KB, 512 KB or 1 MB FPM DRAM (70, 80 or 100ns)
RAMDAC (Internal)
Part # -
See Also CL-GD5402, CL-GD5422 / CL-GD5424

In both the 5420 and 5421, the core clock ran at 75 MHz with memory clocking in at 50 MHz. The chipset offered no GUI acceleration features found in the more advanced CL-GD542x cards from the CL-GD5426 and up. The maximum resolution supported by the chipset was 1024 x 768 (interlaced or non-interlaced) in 256 colours. The chipset provided performance similar to a Tseng Labs ET4000 and was designed to run on ISA bus speeds up to 12.5 MHz.

Video memory was arranged into two banks, accessed via a 16-bit width memory interface. Despite the chipset supporting up to 1 MB of video memory, the vast majority of cards came with either 256 KB or 512 KB, and cards tended to not have sockets for upgradability later on. One exception to this is the Octek AVGA-20 which came with 256 KB soldered-in, but provided four DRAM sockets to upgrade to 512 KB. All CL-GD542x cards beyond the 5420/5421 got a faster 32-bit memory interface.

Here is a summary of the Cirrus Logic CL-GD542x range so you can compare each chipset's differences from one another:

  5420 5421 5422 5424 5425 5426 5428 5429
GUI Acceleration - -         Enhanced BitBLT MM I/O
Max. Video Memory 1 MB 1 MB 1 MB 1 MB 1 MB 2 MB 2 MB 2 MB
Memory Bus Width 16-bit 16-bit 32-bit 32-bit 32-bit 32-bit 32-bit 32-bit
Core Clock Frequency 75 MHz 75 MHz 80 MHz 80 MHz 80 MHz 80 MHz 80 MHz 86 MHz
Memory Clock Frequency 50 MHz 50 MHz 50 MHz 50 MHz 60 MHz 50 MHz 50 MHz 60 MHz
Max. Resolution at 256 Colours 1024 x 768 (NI) 1024 x 768 (NI) 1024 x 768 (NI) 1024 x 768 (NI) 1024 x 768 (NI) 1280 x 1024 1280 x 1024 1280 x 1024


These chipsets can be found on the following cards:

  • Octek AVGA-20 (EP20069R21)
  • AVGA3B
  • Kentech Computer (HK) Ltd (FCC ID: KJDKEN-CL542XVGA) - see pics below
  • VAVGA31-5420-1M (a 1 MB card)
  • Sigma Designs LG240
  • Machspeed VGA 1060-I (FCC ID: KPLO41393)

Cards using this chipset typically worked in either an 8-bit or 16-bit ISA slot, as the chipset had an automatic bus width-sensing capability, along with support for 8-or 16-bit BIOS.



The chipset itself came in these revisions: C.



In direct competition with the CL-GD5420 and 5421 were the Tseng Labs ET4000. Cards with the Cirrus Logic chipset tended to provide better performance than Trident TVGA8900B/C-based cards, though the D-variant of these outperformed it.


In the Media

There is nothing available in the media on this chipset.

Setting it Up

There is no known setup configuration for cards that have a CL-GD5420 / CL-GD5421 chipset.


Operation Manual

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AVGA3 Drivers

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CL-GD542x Databook
Version 7, May 1995

Provides technical information on the entire range of CL-GD542x graphics chipsets.


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More Pictures

Two Kentech CL-GD5420 cards

AVGA3B card

Octek AVGA-20 card