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Chapter 3 Hardware
LittleBoard 550 Reference Manual 37
Pin # Signal Description
All Task File operations occur in byte mode on the low order bus D0-D7, while
all data transfers are 16 bit using D0-D15 to provide the disk data signals.
4 SDD8 Secondary Disk Data 8 – Refer to SDD7 on pin-2 for more information.
5 SDD6 Secondary Disk Data 6 – Refer to SDD7 on pin-2 for more information.
6 SDD9 Secondary Disk Data 9 – Refer to SDD7 on pin-2 for more information.
7 SDD5 Secondary Disk Data 5 – Refer to SDD7 on pin-2 for more information.
8 SDD10 Secondary Disk Data 10 – Refer to SDD7 on pin-2 for more information.
9 SDD4 Secondary Disk Data 4 – Refer to SDD7 on pin-2 for more information.
10 SDD11 Secondary Disk Data 11 – Refer to SDD7 on pin-2 for more information.
11 SDD3 Secondary Disk Data 3 – Refer to SDD7 on pin-2 for more information.
12 SDD12 Secondary Disk Data 12 – Refer to SDD7 on pin-2 for more information.
13 SDD2 Secondary Disk Data 2 – Refer to SDD7 on pin-2 for more information.
14 SDD13 Secondary Disk Data 13 – Refer to SDD7 on pin-2 for more information.
15 SDD1 Secondary Disk Data 1 – Refer to SDD7 on pin-2 for more information.
16 SDD14 Secondary Disk Data 14 – Refer to SDD7 on pin-2 for more information.
17 SDD0 Secondary Disk Data 0 – Refer to SDD7 on pin-2 for more information.
18 SDD15 Secondary Disk Data 15 – Refer to SDD7 on pin-2 for more information.
19 GND Ground
20 NC/Key Not connected / Key pin plug
21 SDREQ Secondary DMA Request – Used for DMA transfers between host and drive
(direction of transfer controlled by DIOR* and DIOW*). Also used in an
asynchronous mode with SDACK*. Drive asserts SDREQ when ready to
transfer or receive data.
22 GND Ground
23 SDIOW*
Secondary I/O Write Strobe – Strobe signal for write functions. Negative edge
enables data from a register or data port of the drive onto the host data bus.
Positive edge latches data at the host.
24 GND Ground
25 SDIOR* Secondary I/O Read Strobe – Strobe signal for read functions. Negative edge
enables data from a register or data port of the drive onto the host data bus.
Positive edge latches data at the host.
26 GND Ground
27 SDIORDY
Secondary I/O Channel Ready – When negated extends the host transfer cycle
of any host register access when the drive is not ready to respond to a data
transfer request. High impedance if asserted.
28 NU Not used (Pull down to ground through 470 ohm resistor)
29 SDDACK* Secondary DMA Acknowledge – Used by the host to acknowledge data has
been accepted or data is available. Used in response to DMARQ asserted.
30 GND Ground
31 IRQ15 Interrupt Request 15 – Asserted by drive when it has pending interrupt (PIO
transfer of data to or from the drive to the host).
32 NC Not connected