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 #	-
	FCC IDs
	Cards
	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
Bus	ISA	ISA	ISA	VLB	VLB	VLB	VLB	VLB
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
ATI VGA
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.

Revisions

The chipset itself came in these revisions: C.

Competition

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.