Vi-2. Main P.c.b - Canon A-200 series Service Manual

VI-2. Main p.e.B.
Figure 6-2 illustrates the block diagram for the main PC.B. Followings are the descriptions for
the LSls used in the A-200. We will use abbreviations hereinafter when describing about these LSls.
• CPU (Central Processing Unit): 8086
16-bit microprocessor; it can access 1 M bytes of memory address and 64K bytes of I/O address
directly.
• NDC (Numeric Data Coprocessor): 8087
This optional lSI is a coprocessor for performing arithmetic operations. The 8087 is to be in­
stalled into the internal 40-pin IC socket with an user's request.
• DMAC (Direct Memory Access Controller): 8237
Control data transfer between I/O devices which are connected to the DMA channels and mem ­
ory without CPU intervention.
The 8237 refreshes dynamic RAMs on the main PC.B. and ones on the optional boards inserted
into the optional slots.
• BCU (Bus Control Unit): 8288
This generates signals necessary for controlling I/O devices and memory by receiving the SO,
S1 and S2 status signals from the CPU.
• PIC (Programmable Interrupt Controller): 8259
Accepts interrupt signals from the I/O devices, and gives priority to one of them. The interrupt
signal selected by the 8259 is sent to the CPU.
• PPI (Programmable Peripheral Interface): 8255
It has three sets of 8-bit input/output ports, and accesses data input from the keyboard or data
set by the DIP switches.
• UART (Universal Asynchronous ReceiverlTransmitter): 8250
Controls the RS-232C interface. Parameters for communication such as baud rate, word length,
stop bit and parity can be controlled by the CPU through this LSI.
• FDC (Floppy Disk Drive Controller): 765
Controls the built-in one or two floppy disk drive(s).
• CG (Clock Generator): 8284
Generates clock signals necessary for the computer. The 8284 also synchronizes the READY
signal with the ClK signal to be sent to the CPU.
• ROM (Read Only Memory): 2764
The A-200 uses two P-ROMs whose respective storage capacity is 8192 words x 8 bits. They
contain power-on self diagnostic program, BIOS, dot patterns for 128 characters in graphics mode
and floppy disk bootstrap loader.
• PIT (Programmable Interval Timer): 8253
Generates an interruptiQn signal when the predetermined timer becomes active and determines
frequency of a signal to be sent to the speaker.
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