22

09/22/00

GL603USB/GL603USB-A/GL603USB-B

Revision 1.4

PORT1.3

4 mA

10K

Ω

PORT1.4

4 mA

10K

Ω

PORT1.5

4 mA (open drain)

PORT1.6

4 mA (open drain)

PORT2.0

4 mA

4K

PORT2.1

4 mA

4K

Ω/8KΩ/16KΩ/32KΩ

PORT2.2

4 mA

4K

Ω/8KΩ/16KΩ/32KΩ

PORT2.3

4 mA

4K

Ω/8KΩ/16KΩ/32KΩ

PORT2.4

4 mA

4K

Ω/8KΩ/16KΩ/32KΩ

PORT2.5

4 mA

4K

Ω/8KΩ/16KΩ/32KΩ

PORT2.6

4 mA

4K

Ω/8KΩ/16KΩ/32KΩ

PORT2.7

4 mA

4K

Ω/8KΩ/16KΩ/32KΩ

Note 1: The pull-down resistor can be configured as 4K

Ω, 8KΩ, 16KΩ or 32KΩ by option-code.

Table 4 -3 General Purpose I/O Port Summary

4.7

TIMER INTERRUPT

The Timer Interrupt is generated when the TIMER register overflows from FFh to 00h. This overflow sets

bit TMROF (INTEN<2>). The interrupt can be masked by clearing bit TMROEN (INTEN<5>). Bit

TMROF must be cleared in software by the Timer module interrupt service routine otherwise the Timer

Interrupt will not be generated again. If prescaler is disabled, the timer register will increase every

instruction cycle. If prescaler is enabled, its increment cycle depends on PS0~PS2 bits in PSCON register.

4.8

USB ENGINE

The USB module contains three functional blocks: a 3.3-volt regulator, a low-speed USB transceiver, and

the Serial Interface Engine (SIE). The USB module is only enabled under USB mode. While the mouse is

working under PS/2 mode, the USB module is disabled and D+/D- working as open drain GPIO pins. The

following details the function of the regulator, transceiver, and SIE.

4.8.1

Voltage Regulator

The USB data lines are required by the USB specification to have a maximum output voltage between 2.8V

and 3.6V. Because the GL603USB is a low speed USB device, the D- lines also are required to have an

external 1.5-k

Ω pull-up resistor connected between a data line and a voltage source between 3.0 V and 3.6

V. Since the power provided by the USB cable is specified to be between 4.4V and 5.0V, an on-chip

regulator is used to drop the voltage to the appropriate level for sourcing the USB transceiver and external

pull-up resistor. An output pin driven by the regulator is provided to source the 1.5-k

Ω external resistor.

4.8.2

USB Transceiver

The USB transceiver provides the physical interface to the USB D+ and D- data lines. The transceiver is

composed of two parts: an output driver circuit and a receiver.

The USB transceiver uses a differential output driver to driver the USB data signal onto the USB cable. The

differential high and low state are well balanced to minimize signal skew. Slew rate control on the driver is

used to minimize the radiated noise and cross talk. The driver’s outputs support 3-state operation to achieve

bi-directional half-duplex operation. The driver can tolerate a voltage on the signal pins of –0.5V to 3.8V

with respect to local ground reference without damage.