Yamaha disklavier MX-100A, Service Manual

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MB8877 (FDC: Floppy Disk Controller)
To enter data on a floppy disk, 8 bits of serial data that is sent from the computer, must be converted
into the corresponding parallel data. To this, again, the clock pulses must be applied. When reading
data from a disk, the same procedure must be repeated, but the reverse order. Floppy disk controller
FDC is, more than anything else, an LSI controlling these operations and also the floopy disk drive.
MB8877 has five internal registers that may be selected by using address lines A0 and A1. Internal
commands may be written on the data I/O terminal to read in data from a diskette or write data on it.
Each time a 1-byte data is read out from a diskette or written on it, the data request (DRQ) line issues
a signal. A signal is issued at the IRQ terminal as soon as the execution of the command ends.
The data to be written on the diskette appears as the output at terminal WD (pin 30). (pin
27 PRD) is the input terminal for data read from the diskette. This data includes clock pulses, though,
only the data read out because of the window pulse entered through the RCLK terminal (pin 26). EARLY
and LATE are the write compensation pulse output terminals indicating whether the write data must be
accelerated or delayed. Terminal TG43 (pin 41) issues signals to indicate whether the head occurs ahead
of or before track 43. The floppy disk drive uses this signal to change the strength of the write current.
Recording density on the outer side of the disks is not the same as that on the inner side, so the write
current must be adjusted to attain a uniform recording characteristic.
Terminal (pin37) is intended to change the format in MB8877 to double density. Pulse output
terminal STEP (pin 1 5) moves the head through a track at a time in the direction determined by the output
at DIRC (pin 46). (pin 34) is an input terminal informing the FDC head is at track 0. (pin 35)
is an input terminal for notifying detection of an index hole.
Signal HLD (pin 28) is meant to press the head on the diskette while terminal HLT (pin 23) indicates
that the head is pressed on the diskette as it should be. Terminal READY (pin 32) indicates that the floppy
disk controller is ready for normal operation.
MB8877 Pin Assignment
Internal address
45