Cypress Semiconductor FX2LP Informazioni Techniche Pagina 378

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EZ-USB FX2 Technical Reference Manual
Page 15-58 EZ-USB FX2 Technical Reference Manual v2.1
Bit 5 LASTRD Last Data Read
To read data over the I²C compatible bus, a bus master floats the SDA line and issues clock
pulses on the SCL line. After every eight bits, the master drives SDA low for one clock to indi-
cate ACK. To signal the last byte of the read transfer, the master floats SDA at ACK time to
instruct the slave to stop sending. This is controlled by setting LastRD=1 before reading the
last byte of a read transfer. The bus controller clears the LastRD bit at the end of the transfer
(at ACK time).
Bit 4-3 ID1:0 Boot EEPROM ID
These bits are set by the boot loader to indicate whether an 8-bit address or 16-bit address
EEPROM at slave address 000 or 001 was detected at power-on. Normally, they are used for
debug purposes only.
Bit 2 BERR Bus Error
This bit indicates a bus error. BERR=1 indicates that there was bus contention, which results
when an outside device drives the bus low when it should not, or when another bus master
wins arbitration, taking control of the bus. BERR is cleared when the IDATA register is read or
written.
Bit 1 ACK Acknowledge Bit
Every ninth SCL or a write transfer the slave indicates reception of the byte by asserting ACK.
The bus controller floats SDA during this time, samples the SDA line, and updates the ACK bit
with the complement of the detected value. ACK=1 indicates acknowledge, and ACK=0 indi-
cates not-acknowledge. The USB core updates the ACK bit at the same time it sets DONE=1.
The ACK bit should be ignored for read transfers on the bus.
Bit 0 DONE Transfer DONE
The bus controller sets this bit whenever it completes a byte transfer, right after the ACK
stage. The controller also generates an Interrupt Request (INT3) when it sets the DONE bit.
The bus controller automatically clears the DONE bit and the Interrupt Request bit whenever
theI2DAT register is read or written.
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