HT49R50 Holtek Semiconductor Inc, HT49R50 Datasheet - Page 25

• Manufacturer Part Number: HT49R50
• Description: 8-Bit Microcontroller
• Manufacturer: Holtek Semiconductor Inc

Input/output ports
There are a 12-bit bidirectional input/output
port, an 8-bit input port in the HT49C50, labeled
PA, PB and PC which are mapped to [12H],
[14H] and [16H] of the RAM, respectively.
PA0~PA3 can be configured as CMOS (output)
or NMOS (input/output) with or without
pull-high resistor by mask option. PA4~PA7 are
always pull-high and NMOS (input/output). If you
choose NMOS (input), each bit on the port
(PA0~PA7) can be configured as a wake-up input.
PB can only be used for input operation, and each
bit on the port can be configured with pull-high re-
sistor. PC can be configured as CMOS output or
NMOS input/output with or without pull-high re-
sistor by mask option. All the port for the input op-
eration (PA, PB and PC), these ports are
non-latched, that is, the inputs should be ready at
the T2 rising edge of the instruction ²MOV A, [m]²
(m=12H or 14H). For PA, PC output operation, all
data are latched and remain unchanged until the
outputlatch is rewritten.
Input/output ports
25
When the PA and PC structures are open drain
NMOS type, it should be noted that, before
reading data from the pads, a ²1² should be
written to the related bits to disable the NMOS
device. That is executing first the instruction
²SET [m].i² (i=0~7 for PA) to disable related
NMOS device, and then ²MOV A, [m]² to get
stable data.
After chip reset, these input lines remain at the
high level or are left floating (by mask option).
Each bit of these output latches can be set or
cleared by the ²SET [m].i² and ²CLR [m].i²
(m=12H or 16H) instructions.
Some instructions first input data and then fol-
low the output operations. For example, ²SET
[m].i², ²CLR [m].i², ²CPL [m]², ²CPLA [m]² read
the entire port states into the CPU, execute the
defined operations (bit-operation), and then
write the results back to the latches or to the ac-
cumulator.
August 18, 1999
HT49C50