Problem with 12F629, servo and EEPROM

[Atom058]

Hello - I am trying to get this VERY simple program to work, but after hours of banging my head on it, I can't see what I am doing wrong. I'm sure that I will be embarrased when someone points out what I need to do...

What I want to do is use a 12F629 to drive a servo via a pot. There are 2 pushbuttons to set the minimum and maximum travel limits for the servo and a switch to enable the user to enter the min and max settings. I can drive the servo with the pot without any problem. The problem arises when I try to set the min and max limits. This process consists of switching the Limit Set Enable slide switch to ON, which pulls GPIO.1 high. This tells the PIC to start monitoring the Min and Max pushbuttons. When the user presses one of the buttons, the PIC takes the current position of the servo and stores it in the appropriate variable and then writes the value to internal EEPROM. After setting the Min and Max values and the Limit Set Enable switch is switched off, the servo movement should be limited to between the min and max limits that were just set. Seems simple enough... What is happening when I set a min or max limit is that the servo will not move from that position. For example, I have the total range of movement set from 100 to 250 (1 to 2.5 ms). I get nice movement over this range. If I move the servo to the middle position (let's say 125) and then enable limit setting and then press the Min button, the movement should then be limited to 125 - 250. Well, it acts as though the min and max limits were both set to 125 - the servo won't move from this position. I'm baffled... Another problem that I am having is that the values for the min and max positions are not being written to the internal memory. I do this so that the PIC will remember the last min/max settings. But when I cycle the power, the settings go back to the original min max values (100 & 250). Following is my code and I have attached my circuit. I would appreciate any insight - again, I fully expect to be embarrased....

@ DEVICE pic12F629, INTRC_OSC_NOCLKOUT ; Using Internal Clock, no clock out
@ DEVICE pic12F629, WDT_ON ; Enable Watch dog timer
@ DEVICE pic12F629, PWRT_ON ; Enable Power-up timer
@ DEVICE pic12F629, MCLR_OFF ; Disable MCLR pin
@ DEVICE pic12F629, BOD_ON ; Enable Brown-out detect
@ DEVICE pic12F629, CPD_OFF ; EEPROM Protect
@ DEVICE pic12F629, PROTECT_OFF ; Code Protect off

TRISIO = %11111110
INTCON.6=0 ' Disable all unmasked Interrupts
INTCON.7=0 ' Disable Global Interrupts
CMCON = 7 ' Disable analog comparator

ServoOut var GPIO.0
SetLimitSw var GPIO.1
PotIn var GPIO.2
MinSw var GPIO.4
MaxSw var GPIO.5

Posit var word
MinPosit var word
MaxPosit var word

'load starting min and max positions at program time
data @ 0, 0, 100
data @ 2, 0, 250

'************************************************* ***************
low Servoout

'read in stored min and max limits
read 0, MinPosit.byte0
read 1, minposit.byte1
read 2, MaxPosit.byte0
read 3, maxposit.byte1

Start:
gosub GetServoPosition
pulsout servoout, posit
pause 20

if setlimitsw = 1 then 'check min max buttons
if minsw = 1 then
MinPosit = Posit
write 0, MinPosit.byte0
write 1, minposit.byte1
pause 250
endif

if maxsw = 1 then
MaxPosit = Posit
write 2, MaxPosit.byte0
write 3, maxposit.byte1
pause 250
endif
endif

goto start

'************************************************* ***************
GetServoPosition:
high potin
pause 1
rctime potin, 1, Posit 'at 4 mhz, returns 0 - 120

'adjust posit to get values between 75 and 250
posit = posit + 75 + (posit / 2)

'now limit posit to 100 - 250 (1 ms - 2.5 ms)
if posit < 100 then posit = 100
if posit > 250 then posit = 250

if setlimitsw = 0 then 'apply limits
if Posit < MinPosit then Posit = MinPosit
if Posit > MaxPosit then Posit = MaxPosit
endif

return

'************************************************* ***************

End