Service manual

Chapter 5 E01S Fault finding
FileStore Service Manual 71
In this application it is programmed to support 250kbps data transfer and MFM decoding. Cl1
and Cl2 are used to adjust the on-chip voltage controlled oscillator. The frequency produced
(on TP2) should 250KHz +/- 12.5% when the FDC is in test mode (see the manufacturers
data sheet).
4.8 The printer /VIA circuitry
IC31 and IC32 control the printer interface. Port A of this device is used to generate a
Centronics parallel type interface with the data buffering by IC32 and strobe by IC21 and
IC22, acknowledge going directly to CA1. Only CB2 of port B is used, as an output to
control the state of the Econet TX/RX clock and terminator circuit. Busy high indicates that
the printer is unable to accept data.
4.9 The FileStore expansion bus and E40S/E60S interface
The FileStore expansion bus appears between locations &FC30 and &FC33. Page &FC is
decoded by 1C23 and IC17. When page &FC is selected a buffer in the data bus (IC30) is
enabled. The direction of this buffer is determined by the read/write line. The read/write line
also selects which set of four outputs on IC35 are used. Page &FC is further decoded into
&FC30 to &FC33 by IC29,
IC34 and IC35. The four locations are as follows.
Address Read Write
&FC30 data data
&FC31 status -
&FC32 - select
&FC33 - enable IRQ
The outputs of IC35 are as follows:
 Y0(pin 15) low - read data or Y4(pin 11) low - write data
Due to the action of Y0 going low IC40 and IC41 will clock a D-type IC33 causing an
acknowledge Signal, this D-type IC33 will be cleared by a request signal returning from
the hard disc drive. The Request / Acknowledge handshake cycle is then complete.
 Y1(pin 14) low - read status When &FC31 is selected, Y1 will go low which enables the
Status Register IC36. All these control signals are inverted by either IC41 or IC42 prior to
being latched, so all values read from the data bus are active high. The control signals
appear in the following table:
DB0 Message
DB1 Busy
DB2 0v
DB3 0v
DB4 NIRQ
DB5 Request
DB6 Input/ Output
DB7 Command/ Data
 Y2(pin 13), Y3(pin 12), Y5(pin 10) are not used.
 Y6(pin 9) low - select
The action of Y6 going low will clock the other half of IC33 causing the select signal to be
produced. This D-type IC33 will be cleared via IC40 and IC41 by the hard disc producing a
busy signal.