UT69RH051 datasheet(3/19 Pages) AEROFLEX

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RST: Reset Input. A high on this input for 24 oscillator periods

while the oscillator is running resets the device. All ports and

SFRs reset to their default conditions. Internal data memory is

undefined after reset. Program execution begins within 12

oscillator periods (one machine cycle) after the RST signal is

brought low. RST contains an internal pulldown resistor to allow

implementing power-up reset with only an external capacitor.

ALE: Address Latch Enable. The ALE output is a pulse for

latching the low byte of the address during accesses to external

memory. In normal operation, the ALE pulse is output every sixth

oscillator cycle and may be used for external timing or clocking.

However, during each access to external Data Memory (MOVX

instruction), one ALE pulse is skipped.

PSEN: Program Store Enable. This active low signal is the read

strobe to the external program memory. PSEN activates every

sixth oscillator cycle except that two PSEN activations are

skipped during external data memory accesses.

EA: External Access Enable. This pin should be strapped to VSS

(Ground) for the UT69RH051.

XTAL1: Input to the inverting oscillator amplifier.

XTAL2: Output from the inverting oscillator amplifier.

2.1 Hardware/Software Interface

2.1.1 Memory

The UT69RH051 has a separate address space for Program and

Data Memory. Internally, the UT69RH051 contains 256 bytes

of Data Memory. It addresses up to 64Kbytes of external Data

Memory and 64Kbytes of external Program Memory.

2.1.1.1 Program Memory

There is no internal program memory in the UT69RH051. All

program memory is accessed as external through ports P0 and

P2. The EA pin must be tied to VSS (ground) to enable access to

external locations 0000H through 7FFFH. Following reset, the

UT69RH051 fetches the first instruction at address 0000h.

2.1.1.2 Data Memory

The UT69RH051 implements 256 bytes of internal data RAM.

The upper 128 bytes of this RAM occupy a parallel address space

to the SFRs. The CPU determines if the internal access to an

address above 7FH is to the upper 128 bytes of RAM or to the

SFR space by the addressing mode of the instruction. If direct

addressing is used, the access is to the SFR space. If indirect

addressing is used, the access is to the internal RAM. Stack

operations are indirectly addressed so the upper portion of RAM

can be used as stack space. Figure 3 shows the organization of

the internal Data Memory.

The first 32 bytes are reserved for four register banks of eight

bytes each. The processor uses one of the four banks as its

working registers depending on the RS1 and RS0 bits in the PSW

SFR. At reset, bank 0 is selected. If four register banks are not

required, use the unused banks as general purpose scratch pad

memory. The next 16 bytes (128 bits) are individually bit

addressable. The remaining bytes are byte addressable and can

be used as general purpose scratch pad memory. For addresses

0 - 7FH, use either direct or indirect addressing. For addresses

larger than 7FH, use only indirect addressing.

In addition to the internal Data Memory, the processor can access

64Kbytes of external Data Memory. The MOVX instruction

accesses external Data Memory.

2.1.2 Special Function Registers

Table 3 contains the SFR memory map. Unoccupied addresses

are not implemented on the device. Read accesses to these

addresses will return unknown values and write accesses will

have no effect.

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