Tandy 102 Service Manual page 100

M2 MI
0 0 Outputs a low-level signal in the latter half (Note 1) of a count period.
0 1 Outputs a low-level signal in the latter half of a count period, automatically loads the pro-
grammed count length, and restarts counting when the TC value is reached.
1 0 Outputs a pulse when the TC value is reached.
1 1 Outputs a pulse each time the preset TC value is reached, automatically loads the pro-
grammed count length, and restarts from the beginning.
Note 1 : When counting an asymmetrical
value such as (9), a high level is output during the first
period of five, and a low level is output during the second period of four.
Note 2: If an internal counter of the 81 C55 receives a reset signal, count operation
stops but the
counter is not set to a specific initial value or output mode. When restarting count opera-
tion after reset, the START command must be executed again through the C/S register.
(6) Standby Mode
The 81 C55 is placed in standby mode when the high level at CE input is latched during the nega-
tive-going edge of ALE. All input ports and the timer input should be pulled up or down to either
Vcc or GND potential.
When using battery back-up, all ports should be set low or in input port mode. The timer output
should be set low. Otherwise, a buffer should be added to the timer output and the battery should
be connected to the power supply pins of the buffer.
By setting the reset input to a high level, the standby mode can be selected. In this case, the com-
mand register is reset, so the ports automatically set to the input mode and the timer stops.