Memory Array; Hardware Functions; Interrupts - HP M2350A Service Manual

Understanding the Computer Module
The Function Cards
Memory Array
The CPC contains four types of memory:
Flash EPROM
The flash EPROM is used for application memory. Flash EPROM is divided into two areas:
the first 1 Mb is configured as a 32 bit wide bank, the remaining 1.5 Mb is configured as an 8
bit wide bank.
The flash EPROM is programmed using the CPC programming tool. The EPROM normally has
VPP set low (between 4.OV and 4.W) and functions as read-only memory. The tool operates
by setting VPP high (12V) and writing an appropriate instruction to the EPROM.
DRAM
The DRAM is used for two purposes: to download programs from the flash EPROM for faster
execution, and to provide unbuffered storage for applications. The DRAM is configured as
three 32 bit wide banks of 1 Mb each. Depending on configuration, the third Mb may be
socketed.
The DRAM refresh is controlled by the microprocessor. A 3.2768 ms timer interrupts the
processor at appropriate intervals for refresh; the processor then writes to a single address
to accomplish the refresh. The DRAM chips have a facility to cycle through the banks each
time a refresh is performed.
Buffered SRAM
The buffered SRAM is used to store application data in the event of a power failure. The
buffered SRAM is configured as one 32 bit wide (512 Kb).bank and two 8 bit wide (256 Kb)
banks. All banks are backed up by a super-capacitor to provide a minimum of three hours of
storage.
Fhst SRAM
The fast SRAM is used primarily for operating system stacks in configurations where
processor performance is critical. The fast SRAM is configured as one 32 bit wide bank.
Hardware Functions
This section describes the basic function of the major components of the CPC, with the
exception of the MPB Interface Chip, which is described in the Master Cards section at the
beginning of this chapter.
Interrupts
The CPC
contains
a support chip to encode interrupts and allow the processor to react to them;
for example, power fail (PFAIL) and external (EXINT) from the local bus.
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