FM8P54E datasheet(7/50 Pages) ETC2

7 / 50 page

FM8P54/56

Rev1.21 May 31, 2005

P.7/FM8P54/56

FEELING

TECHNOLOGY

2.1.2 TMR0 (Time Clock/Counter register)

Address

Name

01h (r/w)

TMR0

8-bit real-time clock/counter

The Timer0 is a 8-bit timer/counter. The clock source of Timer0 can come from the instruction cycle clock or by an

external clock source (T0CKI pin) defined by T0CS bit (OPTION<5>). If T0CKI pin is selected, the Timer0 is

increased by T0CKI signal rising/falling edge (selected by T0SE bit (OPTION<4>)).

The prescaler is assigned to Timer0 by clearing the PSA bit (OPTION<3>). In this case, the prescaler will be cleared

when TMR0 register is written with a value.

2.1.3 PCL (Low Bytes of Program Counter) & Stack

Address

Name

02h (r/w)

PCL

Low order 8 bits of PC

FM8P54/56 devices have a 9-bit (for FM8P54/54E) or 10-bit (for FM8P56/56E) wide Program Counter (PC) and

five-level deep 9-bit (or 10-bit) hardware push/pop stack. The low byte of PC is called the PCL register. This register

is readable and writable. The high byte of PC is called the PCH register. This register contains the PC<9:8> bits and

is not directly readable or writable. All updates to the PCH register go through the PCHBUF register. As a program

instruction is executed, the Program Counter will contain the address of the next program instruction to be executed.

The PC value is increased by one, every instruction cycle, unless an instruction changes the PC.

For a GOTO instruction, the PC<9:0> is provided by the GOTO instruction word. The PCL register is mapped to

PC<7:0>, and the PCHBUF register is not updated.

For a CALL instruction, the PC<9:0> is provided by the CALL instruction word. The next PC will be loaded (PUSHed)

onto the top of STACK. The PCL register is mapped to PC<7:0>, and the PCHBUF register is not updated.

For a RETIA, RETFIE, or RETURN instruction, the PC are updated (POPed) from the top of STACK. The PCL

For any instruction where the PCL is the destination, the PC<7:0> is provided by the instruction word or ALU result.

However, the PC<9:8> will come from the PCHBUF<1:0> bits (PCHBUF

PCH).

PCHBUF register is never updated with the contents of PCH.

FM8P54E Datasheet(PDF) 7 Page - List of Unclassifed Manufacturers