ATARI 260ST
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(pictures copyright by M.A.Grundke)
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ATARI®
ATARI 260ST
ATARI CORP.
MADE IN TAIWANSERIAL NUMBER: A1 4007726 |
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260ST board overview:
beginning on the top left, there's the 40 pin expansion bus connector. Right from it, C025913 (DMA controller, U1), below it the machine's ROM bank (6 pcs. 32KB ROMs at U2-U7). Moving right from the DMA controller is the WD1772 (U9), and again right, the RS232 circuitry (UA1488+UA1489 at U13/U14).
Below these and right from the ROM bank the CPU (U10, biggest DIP-IC on the board) and further below the MC68901 (U11), with MMU (U15, PLCC-pack.) to its right and GLUE (U12, PLCC-pack.) beneath. Right from GLUE are the 16 pcs.256Kx1 DRAMs (U16-U45), forming the RAM bank which extends to the board's right side. Moving up from the RAMs, there's Shifter in its shielding (normally completely shielded, of course), and the internal keyboard connector right from it. Above Shifter is a large free space on the board (that must be where the 520STM has its TV-modulator).
Left from there, finally, are the Yamaha YM2149 with the two ACIAs below it. Note that the board is normally covered by PCB shielding (although not completely - DMA-controller, WDC, RS232 and the Yamaha are not below the shield) |
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board silkscreening:
ATARI® C070243 REV.C |
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| The Motorola MC68000 was probably the most popular 16/ 24 bit-CPU of all time. Internally it processes 32 bits, and was always one step ahead of its Intel counterparts (8086, 80186). As a descendant of the 8 bit Motorola MC6800, it could make use of most of its peripheral devices. There was also a special member of the 680x0-series, the MC68008, which came with an 8 bit data-bus for easily integrating it into existing designs.
It was, as far as I know, only used in the Sinclair QL |
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| The C025915 'GLUE' provides control logic operations to 'glue' together all parts of the ST-architecture |
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| The C025912-38 (some had the C100109) is the memory management unit in the ATARI ST. It can manage a maximum of 4096 KBytes RAM (which was reached in the Mega 4 or the 4160ST, the 4MB-1040ST) |
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| The 260ST's RAM bank, 16 pcs. 256Kx1 DRAMs (Texas Instruments TMS4256 in this case). As mentioned earlier, the 260ST is just a rebadged 520ST, and thus comes with 512 KBytes by default. Reason for this was that ATARI had just introduced the 520ST+, and feared that the remaining quantities of 520STs and its parts could not be sold. So they released the 520ST again, as cheap 'entry-level machine'
called 260ST. However, there was a real 260ST prototype (called 260STd, because it had a diskdrive integrated in its left side), which was quickly abandoned because 256 KBytes are not really enough to work with GEM (that's, by the way, also the reason why the 130ST-project was dropped) |
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This is the ATARI 260ST's ROM bank:
these six chips (C026302-001, C026303-001, C026304-001, C026305-001, C026306-001 and C026307-001) contain the PAL TOS 1.0 |
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| The C025914-38 Shifter is responsible for the ST's graphics. The synonym derives from 'Video Shift Register Chip', because video-modes are set using the so-called 'Shift Mode Register'. Although it's only capable of outputting a maximum of
16 colors (from a 512 colors palette), there were 'hacks' to display all 512 at once |
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| The Yamaha YM2149F is is the ST's soundchip and has three independent voice channels plus noise generator. Some say it's not much better than the AMSTRAD CPC's soundchip, which is not meant as a compliment at all... |
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| The Western Digital WD 1772-PH is the machine's floppy controller. In comparison to its ancestors of the 179x-series, the WD1772 offers stepping rates of 2, 3, 5 and 6 milliseconds |
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| The ST's 'general purpose DMA controller', C025913-38. Despite its name, it is mainly used for floppy- and harddisk-access, together with the onboard floppy controller or an external SCSI harddisk controller. It has the same bus access privileges as the CPU - which device controls the bus is determined via 'first come, first served' |
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| There are two of these Motorola MC6850P in the ATARI ST, which are used for serial I/O (which also includes MIDI) |
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| The ST-series' RS232-circuitry, a Motorola MC1488/ 1489-combination (here produced by National Semiconductor). The 1488 is a so-called 'quad-line driver', the 1489 a 'quad-line receiver'. The driver converts the ST's TTL levels to output levels described in the RS232-standard, allowing to control serial devices. The receiver, as the name implies, provides a RS232-compliant interface for external devices' input |
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| Although this one is obviously produced by Motorola, the 68901 'Multi-Function Peripheral' (MFP) was originally called MK68901 and produced by Mostek. The 68901, however, was designed to be an all-purpose I/O controller for the MC68000's bus and is the descandant of the MK3801, an I/O controller designed for the Z80. It combines 8 parallel I/O lines for devices, a 16 sources interrupt controller, a full duplex USART for serial communication and four timers. In the ST-design
it's main purpose is to generate interrupts for all ports and the keyboard. However, the MFP cannot interrupt the CPU itself, so it signals GLUE that a device needs 'service' (which prioritizes all IRQs and then signals the CPU) |
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On keyboard PCB:
HD6301V1 (C070122), clocked with 1 MHz. Providing basic I/O- and time of day-functions, it is located directly on the keyboard PCB's back. 'Basic I/O' means that it scans the keyboard, does the mouse-tracking and so on, but it can also receive commands from one of the ACIAs. This is what ATARI calls the 'intelligent keyboard' (ikbd) |