MC68302EH20C Freescale Semiconductor, MC68302EH20C Datasheet - Page 420

• Manufacturer Part Number: MC68302EH20C
• Description: IC MPU MULTI-PROTOCOL 132-PQFP
• Manufacturer: Freescale Semiconductor

Specifications of MC68302EH20C

• Processor Type: M683xx 32-Bit
• Speed: 20MHz
• Voltage: 5V
• Mounting Type: Surface Mount
• Package / Case: 132-MQFP, 132-PQFP
• Family Name: M68000
• Device Core: ColdFire
• Device Core Size: 32b
• Frequency (max): 20MHz
• Instruction Set Architecture: RISC
• Supply Voltage 1 (typ): 5V
• Operating Temp Range: 0C to 70C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 132
• Package Type: PQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Lead Free Status / Rohs Status: Compliant

MC68302 Applications
D.9.1 Overview of the Board
The board interfaces two of the MC68302 SCCs to the AppleTalk LAN. SCC1 and SCC2 are
used for this example, but any of the three SCCs could have been originally chosen for use
with the board. The MC68195 LA provides the FM0 encoding/decoding and digital phase-
locked loop functionality. It also provides a direct interface to the MC68302 and the line driv-
er/receiver chips, as shown. The LA input clock is required to be 10x the desired data rate.
Thus, for AppleTallk, a 2.304-MHz crystal was used.
The physical portion of the board was modeled after the Macintosh
Plus serial interface.
Thus, the RS-422 driver/receiver function was implemented with the 26LS32 receiver and
26LS30 line driver. The connectors used were the standard mini-DlN 8, which is the same
as those used in the Macintosh. The connections to this connector followed the Macintosh
Plus serial interface diagram, except that HSKo (pin 1) was simply pulled high through a 100
resistor. This does not inhibit LocalTalk functionality.
D.9.2 Important Side Notes
The reset circuit chosen was a simple RC delay. Normally, the reset function would be part
of the system reset circuitry, but this function was not available through the original connec-
tor on the ADS302 board, so it was built on the LA board. The LA has an internal Schmitt
trigger on the reset input to facilitate this configuration.
Note that there is a pullup on the SCC2 RTS2 pin because SCC2 on the MC68302, unlike
SCC1, has its pins multiplexed with parallel l/O pins. These pins default to the input state
upon reset. If this pullup is omitted, the RTS2 pin might be low between the moment of reset
and the moment at which the software configures this pin to the RTS2 function (i.e., writing
the PACNT register). During this window of time, a low value on RTS2 would cause the LA
to illegally transfer out onto the LocalTalk network. The pullup safely avoids this problem. A
pullup is not needed on the MC68302 RTS1 or RTS3 since they reset to the inactive (high)
state.
Five parallel l/O signals (PA7-PA11) are used to configure the LA into various loopback, by-
pass, or clock enable modes, making it easy for the MC68302 to put the LA into various
modes for testing. In a final implementation, some of these signals could be pulled directly
high or low. As previously described, these signals float until initialized in software by the
MC68302; however, since these briefly floating inputs do not cause a problem in this sys-
tem, pullups and pulldowns were not added.
The channel enable signals (CHEN) were pulled continuously high in this application since
there was no need to disable LA operation. In a final system, these could be easily connect-
ed to MC68302 I/O pins as needed.
.
The general-purpose inputs (GPI) were simply pulled high fort his example. They could
have been used to support asynchronous operation over the mini-DlN 8 connector, if de-
sired.
_________
AppleTalk is a registered trademark of Apple Computer, Inc.
Macintosh is a trademark of Apple Computer, Inc.
D-70
MC68302 USER’S MANUAL
MOTOROLA