Mass Storage - HP 9020 Service Manual

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Theory of Operation
In character mode, character codes from the lOP are loaded into the RAM buffer on the logic
board. When the 81st character is input, or when a Carriage Return, Line Feed, or Backspace
occurs, the buffer is dumped. Each character code is examined in turn, and the character ROM is
accessed to determine the 7 -bit pattern for the particular row being printed. If 80 characters are
being printed, the ROM is accessed 80 times for each row. The 560 bits are serially shifted into the
printhead and printed. Not all dots may be burned in one pass. Two or more passes may be
required, depending on the number of dots to be burned and the average resistance value. Then,
the next row is constructed for the same 80 characters. The process continues until all rows of all 80
characters have been printed. More character codes from the lOP are then loaded into the RAM
buffer, and the process continues.
Mass Storage
Two 5-lj4-inch mass storage devices can be used with the computer. One is a flexible disc drive and
the other a fixed disc drive. The drives and their disc capacities are as follows:
• 9130K Flexible Disc Drive
• Winchester Fixed Disc Drive
264K bytes
10M bytes
The 9130K Flexible Disc Drive must be installed in the upper physical space to the right of the
printer. The Winchester Fixed Disc Drive must be installed in the lower space.
Additional service information for the 9130K can be found in the HP 9130K Flexible Disc Drive
Service Manual, Part No. 09130-90030.
The
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backplane has three mass storage controller slots located below the four
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slots (Figure
2-1). These slots contain the appropriate controller cards for the selected mass storage configura-
tion. Only two of these slots have connectors.
The 9130K Flexible Disc Drive controller card plugs into 70-pin connector P10 on the
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back-
plane. A 34-conductor ribbon cable connected to the outside edge of the controller card provides
drive signals to the flexible disc drive.
The Winchester Fixed Disc Drive controller assembly consists of a card (Winchester
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card) and a
board (Winchester disc controller) physically interconnected in piggyback fashion. The card plugs
into
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backplane connector P11. The attached board occupies the bottom slot space without
being plugged in. The card and board are functionally interconnected by a 50-conductor ribbon
cable and a two-wire power cable. Two connectors on the left edge of the board are interconnected
by ribbon cables to connectors at the front edge of the card. Ribbon cables are routed from the card
connectors to the Winchester Fixed Disc Drive. One is a 20-conductor data cable, and the other a
34-conductor control cable.
The Winchester disc controller contains bootstrap loader circuitry. This is the same circuitry as on
the bootstrap loader card which is used if there is no Winchester disc drive. The circuitry is
described under Bootstrap Loader Card in the
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Backplane section which follows in this chapter.