var A byte, Integer/Word variable or constant that is assigned to the counter.
counterX COUNTER0 , COUNTER1 or COUNTER2.
Use counterX = 0 to reset the counter.
The counter can count from 0 to 255 in mode 2 (8-bit auto reload).
And to 65535 in mode 1(16-bit).
In mode 0 the counter can count to 8192. The MSB and 5 bits of the LSB are used in that case. When you assign a constant to a TIMER/COUNTER in mode 0, the bits will be placed in the right place :
COUNTER0 = &B1_1111_1111_1111_1111 '13 bits
Will be translated for mode 0 into 1111_1111_0001_1111

The counterx variables are intended to set/retrieve the TIMER/COUNTER registers from BASCOM. COUNTER0 = TL0 and TH0.

So the COUNTERx reserved variable is a 16 bit variable.

To set TLx or THx, you can use : TL0 = 5 for example.

Note that the COUNTERx variable operates on both the TIMERS and COUNTER because the TIMERS and COUNTERS are the same thing except for the mode they are working in. To load a reload value, use the LOAD statement.

Important
After access to the counter, the timer/counter is stopped. So when it was running, start it with the statement START COUNTERx

Example
'--------------------------------------------------------------
' (c) 1995-2000 MCS Electronics
'--------------------------------------------------------------
' file: COUNTER.BAS
' demo: COUNTER
'--------------------------------------------------------------
' Connect the timer input P3.4 to a frequency generator
' *TIMER/COUNTER 1 is used for RS-232 baud rate generator
'--------------------------------------------------------------

Dim A As Byte , C As Integer
Config Timer0 = Counter , Gate = Internal , Mode = 1
'Timer0 = counter : timer0 operates as a counter
'Gate = Internal : no external gate control
'Mode = 1 : 16-bit counter

Counter0 = 0 'clear counter
Start Counter0 'enable the counter to count
Do 'set up a loop
A = Inkey() 'check for input
C = Counter0 'get counter value
Print C 'print it
Start TIMER0 'restart the timer
Loop Until A = 27 'until escape is pressed

End

For the next example the ASM code is shown:
COUNTER0 = 1000

Generated code :
Clr TCON.4
Mov tl0,#232
Mov th0,#3