MC68HC05J3 Datasheet, PDF (19/92 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

Providing the oscillator is running at 4MHz, the serial data format is 9600 baud, low start bit, 8
data bits, high stop bit. The data is in hexadecimal form, not ASCII.
2
In the RAM bootloader mode all interrupt vectors are mapped to pseudo-vectors in RAM (refer to
Table 2-2). This allows programmers to use their own service-routine addresses. Each
pseudo-vector is allowed three bytes of space, rather than the two bytes for normal vectors,
because an explicit jump (JMP) opcode is needed to cause the desired jump to the user’s
service-routine address.
Table 2-2 RAM bootloader mode jump vectors
Address Pseudo-vector
0084 Software interrupt
0087 IRQ interrupt
008A Core timer interrupt
008D Input capture
0090 Output compare interrupt
0093 Timer overflow interrupt
2.2
Pin descriptions
OSC1
1
OSC2
2
TCAP/PB5
3
TCMP/PB4
4
PB3
5
PB2
6
PB1
7
PB0
8
VDD
9
VSS
10
20
RESET
19
IRQ
18
PA0
17
PA1
16
PA2
15
PA3
14
PA4
13
PA5
12
PA6
11
PA7
Figure 2-2 20-pin SOIC/DIP single chip and bootloader mode pin assignments
2.2.1 VDD and VSS
Power is supplied to the microcontroller using these two pins. VDD is the positive supply and VSS
is ground.
It is in the nature of CMOS designs that very fast signal transitions occur on the MCU pins. These
short rise and fall times place very high short-duration current demands on the power supply. To
prevent noise problems, special care must be taken to provide good power supply bypassing at
the MCU. Bypass capacitors should have good high-frequency characteristics and be as close to
MC68HC05J3
MODES OF OPERATION AND PIN DESCRIPTIONS
TPG
MOTOROLA
2-3