Specifications

Theory of Operation
DUAL PORT MEMORY
The ZT 8832 is shipped with 32 Kbytes of dual port RAM. Dual port
means that is it accessible by both the ZT 8832 CPU and the STD bus
CPU. The dual port memory is physically separate from the ZT 8832
local memory to permit the local CPU to continue operating even
during a dual port access by the STD bus CPU. It is not until both
CPUs attempt a simultaneous dual port access that arbitration logic
suspends the operation of one CPU until the other is completed. For
continuous accesses by both CPUs, the arbitration logic alternates the
access grant on a machine cycle boundary to ensure both processors
equal time. The arbitration is done entirely in hardware.
While using the dual port is as simple as writing to a standard
memory device, it may be beneficial to implement interrupt driven or
locked transfers. These are supported through the STD bus control
port and the local control port discussed on the following pages. Note
that the dual port RAM is battery backed if the optional battery is
installed.
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