旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � Programming the Trident SVGA Chip � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� Written for the PC-GPE by Mark Feldman e-mail address : u914097@student.canberra.edu.au myndale@cairo.anu.edu.au Please read the file SVGINTRO.TXT (Graphics/SVGA/Intro PC-GPE menu option) 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � THIS FILE MAY NOT BE DISTRIBUTED � � SEPARATE TO THE ENTIRE PC-GPE COLLECTION. � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 旼컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � Disclaimer � 읕컴컴컴컴컴켸 I assume no responsibility whatsoever for any effect that this file, the information contained therein or the use thereof has on you, your sanity, computer, spouse, children, pets or anything else related to you or your existance. No warranty is provided nor implied with this information. 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � Identifying the Trident SVGA Card � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� There are two Trident SVGA chips, the TVGA 8800 and 8900. The Trident SVGA chips can be identified by attempting to change the Mode Control #1 register as follows: Index : 0Eh at port 3C4h Read/write data from port 3C5h 旼컴쩡컴쩡컴쩡컴쩡컴쩡컴쩡컴쩡컴� � 7 � 6 � 5 � 4 � 3 � 2 � 1 � 0 � 읕컴좔컴좔컴좔컴좔컴좔컴좔컴좔컴� � PAGE First write the value 0Eh to port 3C4h. Then read the value in from port 3C5h and save it. for rest Next write the value 00h to port 3C5h and read the value back in from the port. If bit 1 in the value read is set (ie = 1) then a trident chip is present. Finally write the original value back to port 3C5h to leave the SVGA adapter in it's original state. 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � Identifying which Trident Chip is Present � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� The Trident chip can be identified with the following psuedo code : Port[$3C4] := $0B Port[$3C5] := $00 hardware_version_number := Port[$3C5] if hardware_version_number >= 3 then chip is an 8900 else chip is an 8800 This procedure leaves the chip in "New Mode". New Mode and Old mode are discussed below. 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � Trident Graphics Display Modes � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � Mode Resolution Colors Chip � 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � 5Bh 800x600 16 8800/8900 � � 5Ch 640x400 256 8800/8900 � � 5Dh 640x480 256 8800/8900 � � 5Eh 800x600 256 8900 � � 5Fh 1024x768 16 8800/8900 � � 61h 768x1024 16 8800/8900 � � 62h 1024x768 256 8900 � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 旼컴컴컴컴컴컴컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � Trident Display Memory � 읕컴컴컴컴컴컴컴컴컴컴컴켸 Both Trident chips can map video memory in either 64K or 128K paging schemes. The 8800 defaults to the 128K paging scheme at power up. This scheme is known as the "Old Mode". The 8900 defaults to the 64K paging scheme, the "New Mode". This file will concentrate solely on the 64K new mode operation. The new mode can be set with the following procedure: Port[$3C4] := $0B { Set the old mode 128K scheme } Port[$3C5] := $00 dummy_variable := Port[$3C5] { Toggle over to the new mode } Trident bank switching is weird, REALLY weird! In new mode, the New Mode Control Register # 1 is used to select the active bank: Index : 0Eh at port 3C4h Read/write data from port 3C5h 旼컴쩡컴쩡컴쩡컴쩡컴쩡컴쩡컴쩡컴� � 7 � 6 � 5 � 4 � 3 � 2 � 1 � 0 � 읕컴좔컴좔컴좔컴좔컴좔컴좔컴좔컴� 읕쩡� � � Bank Page Seg Bits 3-0 can be considered as a single 4 bit bank number. However, when you write to video memory the Trident inverts the Page bit to determine which bank should actually be written to. So if you set these bits to the value 0 (0000) then bank 0 will be used for all read operations and bank 2 (0010) will be used for all write operations. The following code will set the bank number for all read operations: PortW[$3C4] := bank_number shl 8 + $0E; The following code will set the bank number for all write operations: PortW[$3C4] := (bank_number xor 2) shl 8 + $0E; It is important to realise that setting the write bank number changes the read bank number, and visa-versa. How you are supposed to rapidly transfer blocks of data around on the Trident screen is beyond me.