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Clock/Calendar
PS2 Keyboard Port
The Three Stooges
Startup Self Identification
Revision E
Equipment Overview: Theory of Operation
onslaught, so no external ESD protection is provided. The transceivers may be shut
down under software control to conserve power.
The Super I/O device provides a clock /calendar function. Backup battery power is
provided by a "super" capacitor (C21) with sufficient storage capacity to power the
clock for hours after main battery removal. This backup source provides sufficient
time to exchange battery packs when necessary. Diode CR106 charges C21 when
the main system power is up. R179 limits the charging current to a safe level.
External card / bar code readers may be connected to the MAC 5500 via a PS-2
compatible keyboard port. A small amount of 5V power is available at the connector
to power the external device. Power faults are detectable. EMI and ESD protection
are provided.
System management and some low level I/O functions are implemented in
preprogrammed 68HC05 microcontrollers. Moving some I/O functions out into
small processors relieves the ATMEL CPU of burdensome real-time chores and
moves the control hardware closer to the controlled devices, potentially reducing
EMI. Localizing control also promotes reuse in future designs as the functions are
self contained and reasonably portable.
Originally there were four Stooges. Since the boot loading and FPGA configuration
is handled by ATMEL CPU, the Curly was removed in -006 board. Although there
are three of these little fellows in the MAC 5500, each performing a different
function, there is only one firmware image. By merging the code from each of the
three functions into a single ROM image, cost and confusion are reduced. It is
impossible to place a processor in the wrong spot on the board and a single pile of
paperwork supports all of the MAC 5500's 68HC05 production volume. More
detailed information may be found in the source code.
As each controller is released from reset, it executes a common "WhoAmI" routine
to determine its identity on the board. Each controller's environment is uniquely and
easily identified with a few port pin tests. Once the identity is discovered, the code
jumps to the appropriate entry point in the unified image and microcontroller
assumes the desired personality.
The flow for the "WhoAmI" routine is as follows:
Run ChkMoe: Basically if the BBus (PD5) is low we are Moe. Since Moe
controls the power supply for +3V-M which is off at the moment, the BBus
pull-up resistors will actually pull the BBus lines low. This can only occur with
Moe since all other Stooges are powered by +3V-M, Moe is powered by +3V-C
instead.
Run ChkCurly: Though the Curly is removed, the firmware related to Curly is
still present, for backward compatibility.
MAC 5500 resting ECG analysis system
2020299-020
2-29
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