SECTION 2 HARDWARE DESCRIPTION
3
SECTION 2
HARDWARE DESCRIPTION
2.1 OVERVIEW
The operational characteristics of the DOUBLE D are a
function of both hardware and on-board software. The hardware
provides the data paths, logic functions, and control signals
necessary to implement such operations as head loading, drive
selection, head positioning, and transferring data. It is the
software that determines how the disk controller commands are
interpreted and in what sequence controller events-take place.
As in all microprocessor designs, the software can do no more
than hardware implementation allows. The DOUBLE D is designed to
allow the on-board software as much control as possible. For the
user who will write control programs for this board, an
understanding of the hardware is recommended. This section
provides a description of the hardware.
2.2 MEMORY ADDRESS DECODING
The S-100 bus address lines are constantly monitored by the
Memory Address Detection circuit. See Figure 2-1. In the
Standard address mode, ICs 3H and 3B implement detection of the
selected 1K memory block. Switches M10, M11, and M12 are used
to locate the selected memory block on any 1K boundary from EOOO
to FCOO. Note: Signals SA10, SA11, and SA12 indicate the
corresponding address switch settings. See Table 2-1. For the
Extended Address Mode, IC 4B must be installed and the Address
Mode Block altered to the appropriate position. In this
configuration, address decoding is provided for any 1K block in
the upper 8K of the 24 bit address bus. In either mode, an
address match is indicated by BMA* (Bus - Memory Addressed)
being asserted (low).
SWITCH
M12
SWITCH
M11
SWITCH
M10
SA12 SA11 SA10 ADDRESS RANGE
IN THE SYSTEM
Closed Closed Closed 0 0 0 EOOO - E3FF
Closed Closed Opened 0 0 1 E400 - E7FF
Closed Opened Closed 0 1 0 E800 - EBFF
Closed Opened Opened 0 1 1 ECOO - EFFF
Opened Closed Closed 1 0 0 FOOO - F3FF
Opened Closed Opened 1 0 1 F400 - F7FF
Opened Opened Closed 1 1 0 FEOO - FBFF
Opened Opened Opened 1 1 1 FCOO - FFFF
Table 2-1. Memory Address Selection
(123 Seiten)
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