68HC16MOD-16WIDE
68HC16MOD-16WIDE
2 _______________________________________________________________________________________
The 68HC16MOD-16WIDE module uses a phase-locked
loop (PLL) to set its bus speed. Crystal Y1 is a
32.768kHz frequency reference. The internal oscillator
runs 256 times faster than the external crystal. When the
68HC16MOD-16WIDE module is reset, it waits for the
PLL to lock before it executes any software. After the
PLL locks onto the reference frequency, the software
doubles the clock speed by writing to the clock synthe-
sizer control register, selecting a bus speed of
16.78MHz.
U5 and U8, the user RAM area, are 32kbyte CMOS stat-
ic RAMs.
The 74HCT245 octal buffers let the 68HC16MOD-
16WIDE module access a 16-bit port on the interface
connectors. This memory-mapped port consists of sep-
arate read and write strobes, four chip selects, four
address LSBs, and sixteen data bits.
Serial Communications
J3 is an RS-232 serial port, designed to be compatible
with the IBM PC 9-pin serial port. Use a straight-
through DB9 male-to-female cable to connect J3 to this
port. If the only available serial port has a 25-pin con-
nector, you may use a standard 25-pin to 9-pin
adapter. Table 1 shows the pinout of J3.
The MAX233 is an RS-232 interface voltage level-shifter
with two transmitters and two receivers. It includes a
built-in charge pump with internal capacitors that gener-
ates the output voltages necessary to drive RS-232 lines.
40-Pin Connectors P1 and P2
The 20 x 2 pin headers (P1 and P2) connect the
68HC16MOD-16WIDE module to a Maxim EV kit. Table
2 lists the function of each pin.
Address Ranges
The 68HC16 µC generates various enable signals for
different address ranges. The ROM and RAM enable
signals are fed directly to the respective chips. Several
additional signals (P1–33 to P1–36) are available on the
data connector to be used by Maxim EV kits. Table 3
outlines the address ranges for each of the elements
found on the 68HC16MOD-16WIDE module, and Table
4 is a truth table that describes the logic for each of the
module’s chip-select outputs. Because the addresses
are not completely decoded, the boot ROM and has a
shadow at address 08000 hex.
Boot ROM
The boot ROM, U3, is configured as an 8-bit memory
device. Resistor R4 pulls data bit 0 low during system
reset, forcing the µC to fetch instructions using only the
upper eight data bits. The boot ROM checks the system
and waits for commands from the host. Refer to the EV
kit manual for specific start-up procedures.
Software
All software is supplied on a disk with the EV kit.
Instructions for operating the software are included in
the EV kit manual. Refer to the EV kit manual for more
information.
Use the 68HC16MOD-16WIDE module only with those
EV kits that are designed to support it, and only down-
load code that is targeted for the 68HC16MOD-16WIDE
module. Downloading incorrect object code into the
68HC16MOD-16WIDE module will have unpredictable
results.
UnusedNone9
Handshake; hard-wired to RTSCTS8
Handshake; hard-wired to CTSRTS7
Handshake; hard-wired to DCD and DTRDSR6
Signal ground connectionGND5
Handshake; hard-wired to DCD and DSRDTR4
RS-232-compatible data input to
68HC16MOD-16WIDE module
TXD3
Handshake; hard-wired to DTR and DSRDCD1
FUNCTIONNAMEPIN
RS-232-compatible data output from
68HC16MOD-16WIDE module
RXD2
Table 1. Serial Communications Port J3
