HC05 datasheet(27/232 Pages) MOTOROLA

27 / 232 page

MC68HC05X16

Rev. 1

MOTOROLA

2-3

MODES OF OPERATION AND PIN DESCRIPTIONS

Note:

Oscillator divide-by-two is forced in bootstrap mode; all other mask options are selected

by the customer (see Section 1.2).

2.1.2.1

Serial RAM loader

In the ‘load program in RAM and execute’ routine, user programs are loaded into MCU RAM via

the SCI port and then executed. Data is loaded sequentially, starting at RAM location $0050, until

the last byte is loaded. The ﬁrst byte loaded is the count of the total number of bytes in the program

plus the count byte. After completion of RAM loading, control can be transferred either to the

second byte in RAM, $0051, by executing a jump to RAM + 1 function, or it can be transferred to

any address by executing a jump to any address function. During the ﬁrmware initialization stage,

the SCI is conﬁgured for the NRZ data format (idle line, start bit, eight data bits and stop bit). The

baud rate is 9600 with a 4 MHz crystal. A program to convert ASCII S-records to the format

required by the RAM loader is available from Motorola.

When the last byte is loaded, the ﬁrmware halts operation expecting additional data to arrive. At

this point, the reset switch is placed in the reset position which resets the MCU, but keeps the RAM

program intact. All routines loaded in RAM can now be entered from this state, including the one

which executes the program in RAM (see Section 2.1.2.2 and Section 2.1.2.3).

To load a program in the EEPROM, the ‘load program in RAM and execute’ function is also used.

In this instance the process involves two distinct steps. Firstly, the RAM is loaded with a program

which controls the loading of the EEPROM, and when the RAM contents are executed, the MCU

is instructed to load the EEPROM.

The erased state of the EEPROM is $FF.

Figure 2-3 shows the schematic diagram of the circuit required for the serial RAM loader.

2.1.2.2

Jump to RAM + 1

After the serial RAM loader program is completed this function can be used to execute a program

loaded in RAM starting at the second RAM address, $0051. It must be noted that the lowest RAM

address, $0050, is used by the RAM loader program to store the total number of bytes in the

program.

2.1.2.3

‘Jump to any address’

This function allows execution of programs previously loaded in RAM or EEPROM using the

methods outlined in Section 2.1.2.1.

To execute the ‘jump to any address’ function, data input at port A has to be $CC and data input at

port B and port C should represent the MSB and LSB respectively, of the address to jump to for

execution of the user program. A schematic diagram of the circuit required is shown in Figure 2-2.

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