Download

PDF Abstract Text:

EZ-USB IO Ports

EZ-USB IO Port Details

EZ-USB IO Ports
Introduction
EZ-USB IO Port Details
Figure 1 shows the basic structure of an EZ-USB IO pin, followed by the registers for PORTA. There are corresponding registers for PORTB and PORTC.
Alternate Function
Figure 1. EZ-USB Input / Output Pin
Port A Output Enable b4 OEA4 b3 OEA3
Port A Outputs b4 OUTA4 b3 OUTA3
Port A Pins
Cypress Semiconductor Corporation
3901 North First Street
San Jose
CA 95134
408-943-2600 February 2, 2000
EZ-USB IO Ports
EZ-U SB
SFR 0x92
Figure 2. Different Registers Supply Upper Address A15.8
Listing
EZ-USB IO Ports
org 100h ------------------------start: mov SP, #STACK-1 set stack mov dptr, #PORTCCFG mov a, #11000000b read and write strobes movx @dptr, a mov dptr, #OEC output enables, port C movx @dptr, a same bits, b7-b6 mov a, #80H somewhere in external memory mov MOVXPAGE, a MPAGE register at 92H loop: movx @r0, a write r0 to data bus inc a sjmp loop END
The MOVXPAGE register is initialized to an off-chip upper address byte of 0x80 in line 30. Then a continuous loop writes the accumulator to external memory, increments the accumulator, and repeats. This example is meant only to show the timing of the data and WR# strobes, so the contents of R0 are unimportant. Normally R0 would also be initialized to reflect the lower external address byte. Figure 3 shows the WR# line and bit 0 of the data bus for the example code. The D0 line toggles for every write, as expected.
Figure 3. Waveforms for WR# and Data Bus