ht82k68e-l Holtek Semiconductor Inc., ht82k68e-l Datasheet - Page 14

• Manufacturer Part Number: ht82k68e-l
• Description: Ht82k68e-l/ht82k68a-l -- Multimedia Keyboard Encoder 8-bit Mcu
• Manufacturer: Holtek Semiconductor Inc.

In the timer mode, once the timer counter starts count-
ing, it will count from the current contents in the timer
counter to FFH. Once overflow occurs, the counter is re-
loaded from the timer counter preload register and gen-
erates the interrupt request flag (TF; bit 5 of INTC) at the
same time.
To enable the counting operation, the timer ON bit
(TON; bit 4 of TMRC) should be set to 1. In the case of
timer counter OFF condition, writing data to the timer
counter preload register will also reload that data to the
timer counter. But if the timer counter is turned on,
data written to it will only be kept in the timer counter
preload register. The timer counter will still operate until
overflow occurs. When the timer counter (reading TMR)
is read, the clock will be blocked to avoid errors. As
clock blocking may results in a counting error, this must
be taken into consideration by the programmer.
Input/Output Ports
There are 34 bidirectional input/output lines in the
microcontroller, labeled from PA to PE, which are
mapped to the data memory of [12H], [14H], [16H],
[18H] and [1AH] respectively. All these I/O ports can be
used for input and output operations. For input
operation, these ports are non-latching, that is, the
inputs must be ready at the T2 rising edge of instruction
MOV A,[m] (m=12H, 14H, 16H, 18H or 1AH). For output
operation, all data is latched and remains unchanged
until the output latch is rewritten.
Each I/O line has its own control register (PAC, PBC,
PCC, PDC, PEC) to control the input/output configura-
tion. With this control register, CMOS output or Schmitt
trigger input with or without pull-high resistor (mask op-
tion) structures can be reconfigured dynamically (i.e.,
on-the-fly) under software control. To function as an
input, the corresponding latch of the control register must
Rev. 1.10
Input/Output Ports
14
write 1 . The pull-high resistance will exhibit automatically
if the pull-high option is selected. The input source(s) also
depend(s) on the control register. If the control register bit
is 1 , input will read the pad state. If the control register bit
is 0 , the contents of the latches will move to the internal
bus. The latter is possible in read-modify-write instruc-
tion. For output function, CMOS is the only configuration.
These control registers are mapped to locations 13H, 15H,
17H, 19H and 1BH.
After a chip reset, these input/output lines stay at high
levels or floating (mask option). Each bit of these in-
put/output latches can be set or cleared by the SET [m].i
or CLR [m].i (m=12H, 14H, 16H, 18H or 1AH) instruction.
Some instructions first input data and then follow the
output operations. For example, the SET [m].i, CLR
[m].i, CPL [m] and CPLA [m] instructions read the entire
port states into the CPU, execute the defined operations
(bit-operation), and then write the results back to the
latches or the accumulator.
Each line of port A and port C [0:3] has the capability to
wake-up the device.
PC2 is shared with the external interrupt pin, PE2~PE4
is defined as CMOS output pins only. PE0 can deter-
mine whether the high to low transition, or the low to
high transition of PC2 to activate the external subrou-
tine, when PE0 output high, the low to high transition of
PC2 to trigger the external subroutine, when PE0 output
low, the high to low transition of PC2 to trigger the exter-
nal subroutine.
PE2~PE4 is configured as CMOS output only and is
used to drive the LED. PC0, PC1 is configured as
NMOS open drain output with 4.6k
such that it can easy to use as DATA or CLOCK line of
PS2 keyboard application.
HT82K68E-L/HT82K68A-L
pull-high resistor
April 2, 2008