Page 136 - Embedded Microprocessor Systems Real World Design

INT2: 16550 interrupt
INT3: Unused
Port bits: Does not apply to the example used here, but in a microcontroller
design, you would describe the usage of the port bits:
RBO: Interrupt from external pushbutton
RB1: Turns on diagnostic LED (0 = LED on)
RB2-Rl37: Unused
RCO-RC7: Communication FIFO data bus
This description also would apply to a multichip design that used a PI0 chip
or had discrete 1/0 ports implemented in a PLD. Similar descriptions are
needed for other software-controlled functions. If the design includes
ADCs or DACs, spec@ the range in bits and how it corresponds to what is
being measured or controlled. For example, an &bit ADC measuring
pressure might be specified as representing 1OOpsi at full scale.
Interface Protocol. If the board communicates with an external system, this
describes the protocol used.
Appendix. If there are calculations that went into the design, such as required
motor torque or interface throughput requirements, these are collected into
an appendix.

A Note About Electronic Parts

This chapter and the previous chapter have covered numerous ICs that can be used
to interface to microprocessors. The electronics world seems to be defined by
shorter product lives, bigger memories, and faster processors. Although the spe-
cific techniques described here may be implemented in a CPLD, FPGA, or ASIC
and access times get ever shorter, the basic design principles still apply.

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