5
Step 13
Bridge solder Pad J5 using a small blob of solder. This will connect the SRAM supply to VCC. J5 is
located on the bottom side of the board, near JP4.
Note:
If you plan to use a standard 256kbit SRAM memory chip and not a Dallas battery backed memory
module, do not bridge solder pad J5. See step 22 for optional external SRAM battery backup.
Step 14
You should wash and clean the completed board before installing U3 and U4. We use water soluble
flux solder here at EAS. This permits easy board cleaning. Radio Shack sells flux removing solvent
made for pc board cleaning. Take a close look at all solder joints and touch-up any joints that look
bad. A 2x or 3x magnifying glass helps to find any solder bridges.
When installing the 68HC11 processor, observe pin one polarity. Some PLCC sockets may require
firm pressure when pushing in the processor. Also observe proper pin placement when install the
memory module.
U4 - MC68HC11A1FN CPU
U3 - DS1230AB/Y Dallas 256kbit (32Kbyte) battery backed static ram. Substitute a DS1244Y if a real
time clock is needed. You can also use a Dallas DS1216D 28pin lithium battery socket but will need
separate 256kbit 62256-100LP static memory chip.
Note:
If you are using a header for JP6, place a couple of jumper shunts on JP6. This is the A/D reference
input voltage. Install a shunt across pins 1 and 2 to tie VRH to VCC. Install a shunt across pins 3 and
4 to tie VRL to ground.
A small hole is provided underneath the 68HC11 to be used to remove the processor. Use a small
diameter screwdriver to push the processor out of the IC socket.
Communications Board Assembly
Step 15
Install U8 on the Communications printed circuit board. Observe proper orientation for pin 1. If you
want, you can install an IC socket for U8.
U8 - MAX232CPE (Maxim)
Note: We have noticed when using 3
rd
party manufactured equivalent Maxim MAX232CPE chips,
downloading S19 files from DOS isn’t as reliable. Please purchase exact Maxim part for the
Communications Board.
Step 16
Install capacitors C8, C9, C10, C11, C12. Observe the polarity of the capacitors before soldering.
C8, C9, C10, C11, C12 - 1uf tantalum 16 volt or greater.
Step 17
Install resistor R7 and LED D1. The shorter lead on LED D1 is the cathode. If D1 is installed
