MO SEL VITELIC
MSU2051/U2031
#EA
Pin Descriptions
Vss
When held at a TTL high level, the MSU2051 executes
instructions from the internal ROM when the PC is less
than 4096. When held at a TTL low level, the
MSU2051 fetches all instuctions from external Program
Memory.
Circuit ground potential.
VDD
+3V (or +5 V) power supply during operation.
XTAL 1
PORT 0
Input to the oscillator's high gain amplifier. A crystal or
external source can be used.
Port 0 is an 8-bit open drain bidirectional I/O port.
It is also the multiplexed low-order address and data
bus when using external memory.
XTAL 2
Output from the oscillator's amplifier. Required when a
crystal is used.
PORT 1
Port 1 is an 8-bit quasi-bidirectional I/O port with
internal pull-up resistance.
Terms
PORT 2
Idle Mode
Port 2 is an 8-bit quasi-bidirectional I/O port with
internal pull-up resistance. It also emit the high-order
address byte when accessing external memory.
During idle mode, the CPU is stopped but below blocks
are kept functioning: clock generator, RAM, timer/
counters, serial port and interrupt block. To save power
consumption, user's software program can invoke this
mode. The on-chip data RAM retains the values during
this mode, but the processor stops executing
instructions. In Idle mode (IDL=1), the oscillator
continues to run and the interrput, and timer blocks
continue to be clocked but the clock signal is gated off
to the CPU. The activities of the CPU no longer exist
unless waiting for an interrupt request.
-An instruction that sets flag (PCON.0) causes that to be
the last instruction executed before going into the Idle
Mode.
-In the Idle Mode, the internal clock signal is gated off to
the CPU, but not to the interrupt, Timer function.
-The CPU status is entirely preserved in its:
the Stack Pointer, Program Counter, Program Status
Word, Accumulator, and all other registers maintain
their data during Idle mode.
PORT 3
Port 3 is an 8-bit quasi-bidirectinal I/O port with internal
pull-up resistance. It also contains the interrupt, timer,
serial port and #RD as well as #WR pins that are used
by various options. The output latch corresponding to a
secondary function must be programmed to one (1) for
that function to operate. The secondary functions are
assigned to the pins of port 3, as follows:
- RXD/data (P3.0). Serial port's transmitter data output
(asynchronous) or data input/output (asynchronous).
- TXD/clock (P3.1). Serial port's transmitter data
output (asynchronous) or data output (asynchronous).
- #INT0 (P3.2). Interrupt 0 input or gate control input
for counter 0.
- #INT1 (P3.3). Interrupt 1 input or gate control input
for counter 1.
- T0 (P3.4). Input to counter 0.
- T1 (P3.4). Input to counter 1.
-There are three ways to terminate the Idle Mode.
1) By interrupt
Activation of any enabled interrupt will cause flag
(PCON.0) to be cleared by hardware, termination the
Idle Mode. After the program wakes up, the PC value
will point as interrupt vector (if enable IE register) and
execute interrupt service routine then return to PC+1
address after the program wakes up.
- #WR (P3.6). The write control signal latches the data
byte from Port 0 into the External Data Memory.
- #RD (P3.7). The read control signal enables External
Data Memory to Port 0.
RES
2) By hardware reset
Since the clock oscillator is still running, the hardware
reset needs to be held active for only two machine
cycles (24 oscillator periods) to complete the reset. All
SFR and PC value will be cleared to reset value.
3) By one of CLK, DATA, PORT 2.0-2.7 transition to
low (falling edge trigger)
After the program wakes up, the PC value will be
0023h (if enable IE register) and execute interrupt
service routine and then returns to PC+1 address after
the program wakes up.
A high on this pin for two machine cycles (24 clocks)
while the oscillator is running, resets the device. The
data in RAM is preserved when reset signals - reset
does not clear the data in RAM.
ALE
Provides Address Latch Enable output used for latching
the address into external memory during normal opera-
tion.
#PSEN
The Program Store Enable output is a control signal that
enables the external Program Memory to the bus during
normal fetch operations.
Rev. 1.0 February 1998
5
MOSEL [ MOSEL VITELIC, CORP ]
