COP888CF Datasheet, PDF (14/44 Pages) National Semiconductor (TI) – 8-Bit CMOS ROM Based Microcontrollers with 4k Memory and A/D Converter

Pin Descriptions (Continued)
Port G is an 8-bit port with 5 I/O pins (G0, G2–G5), an input
pin (G6), and two dedicated output pins (G1 and G7). Pins
G0 and G2–G6 all have Schmitt Triggers on their inputs. Pin
G1 serves as the dedicated WDOUT WatchDog output,
while pin G7 is either input or output depending on the oscil-
lator mask option selected. With the crystal oscillator option
selected, G7 serves as the dedicated output pin for the CKO
clock output. With the single-pin R/C oscillator mask option
selected, G7 serves as a general purpose input pin, but is
also used to bring the device out of HALT mode with a low to
high transition on G7. There are two registers associated
with the G Port, a data register and a configuration register.
Therefore, each of the 5 I/O bits (G0, G2–G5) can be indi-
vidually configured under software control.
Since G6 is an input only pin and G7 is the dedicated CKO
clock output pin or general purpose input (R/C clock configu-
ration), the associated bits in the data and configuration reg-
isters for G6 and G7 are used for special purpose functions
as outlined below. Reading the G6 and G7 data bits will re-
turn zeros.
Note that the chip will be placed in the HALT mode by writing
a “1” to bit 7 of the Port G Data Register. Similarly the chip
will be placed in the IDLE mode by writing a “1” to bit 6 of the
Port G Data Register.
Writing a “1” to bit 6 of the Port G Configuration Register en-
ables the MICROWIRE/PLUS to operate with the alternate
phase of the SK clock. The G7 configuration bit, if set high,
enables the clock start up delay after HALT when the R/C
clock configuration is used.
Config Reg.
Data Reg.
G7
CLKDLY
HALT
G6
Alternate SK
IDLE
Port G has the following alternate features:
G6 SI (MICROWIRE™ Serial Data Input)
G5 SK (MICROWIRE Serial Clock)
G4 SO (MICROWIRE Serial Data Output)
G3 T1A (Timer T1 I/O)
G2 T1B (Timer T1 Capture Input)
G0 INTR (External Interrupt Input)
Port G has the following dedicated functions:
G7 CKO Oscillator dedicated output or general purpose
input
G1 WDOUT WATCHDOG and/or Clock Monitor dedicated
output.
Port C is an 8-bit I/O port. The 40-pin device does not have
a full complement of Port C pins. The unavailable pins are
not terminated. A read operation for these unterminated pins
will return unpredictable values.
Port I is an 8-bit Hi-Z input port, and also provides the analog
inputs to the A/D converter. The 28-pin device does not have
a full complement of Port I pins. The unavailable pins are not
terminated (i.e. they are floating). A read operation from
these unterminated pins will return unpredictable values.
The user should ensure that the software takes this into ac-
count by either masking out these inputs, or else restricting
the accesses to bit operations only. If unterminated, Port I
pins will draw power only when addressed.
Port D is an 8-bit output port that is preset high when RESET
goes low. The user can tie two or more D port outputs (ex-
cept D2) together in order to get a higher drive.
Note: Care must be exercised with the D2 pin operation. At RESET, the ex-
ternal loads on this pin must ensure that the output voltages stay
above 0.8 V_CC to prevent the chip from entering special modes. Also
keep the external loading on D2 to less than 1000 pF.
Functional Description
The architecture of the device is modified Harvard architec-
ture. With the Harvard architecture, the control store pro-
gram memory (ROM) is separated from the data store
memory (RAM). Both ROM and RAM have their own sepa-
rate addressing space with separate address buses. The ar-
chitecture, though based on Harvard architecture, permits
transfer of data from ROM to RAM.
CPU REGISTERS
The CPU can do an 8-bit addition, subtraction, logical or shift
operation in one instruction (t_c) cycle time.
There are five CPU registers:
A is the 8-bit Accumulator Register
PC is the 15-bit Program Counter Register
PU is the upper 7 bits of the program counter (PC)
PL is the lower 8 bits of the program counter (PC)
B is an 8-bit RAM address pointer, which can be optionally
post auto incremented or decremented.
X is an 8-bit alternate RAM address pointer, which can be
optionally post auto incremented or decremented.
SP is the 8-bit stack pointer, which points to the subroutine/
interrupt stack (in RAM). The SP is initialized to RAM ad-
dress 06F with reset.
All the CPU registers are memory mapped with the excep-
tion of the Accumulator (A) and the Program Counter (PC).
PROGRAM MEMORY
Program memory consists of 4096 bytes of ROM. These
bytes may hold program instructions or constant data (data
tables for the LAID instruction, jump vectors for the JID in-
struction, and interrupt vectors for the VIS instruction). The
program memory is addressed by the 15-bit program
counter (PC). All interrupts vector to program memory loca-
tion 0FF Hex.
DATA MEMORY
The data memory address space includes the on-chip RAM
and data registers, the I/O registers (Configuration, Data and
Pin), the control registers, the MICROWIRE/PLUS SIO shift
register, and the various registers, and counters associated
with the timers (with the exception of the IDLE timer). Data
memory is addressed directly by the instruction or indirectly
by the B, X and SP pointers.
The device has 128 bytes of RAM. Sixteen bytes of RAM are
mapped as “registers” at addresses 0F0 to 0FF Hex. These
registers can be loaded immediately, and also decremented
and tested with the DRSZ (decrement register and skip if
zero) instruction. The memory pointer registers X, SP, and B
are memory mapped into this space at address locations
0FC to 0FE Hex respectively, with the other registers (other
than reserved register 0FF) being available for general us-
age.
The instruction set permits any bit in memory to be set, reset
or tested. All I/O and registers (except A and PC) are
memory mapped; therefore, I/O bits and register bits can be
directly and individually set, reset and tested. The accumula-
tor (A) bits can also be directly and individually tested.
Note: RAM contents are undefined upon power-up.
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