TCC720 Datasheet, PDF (133/143 Pages) List of Unclassifed Manufacturers – 32-bit RISC Microprocessor For Digital Media Player

TCC720
32-bit RISC Microprocessor for Digital Media Player
Dec. 16. 2002
BOOTING PROCEDURE
Preliminary Spec 0.51
14.2 UART Boot
For the flexibility and safety of code transfer, there are 2 modes in TCC720 for selecting UART
clock. One is using XIN clock divided by 8, the other is using XTIN clock.
This can be selected by setting GPIO_A[10:8] appropriately as described in table 14.1.
Normally, the frequency of UART need to be about 3.6864MHz. But that of XIN may be variable
according to the applications. To compromise the difference of clock between TCC720 and host
(most case it is a desktop PC), the code is transferred by 1 bit per 1 byte transmission. That is,
although the UART transmission is accomplished by 1 byte unit, TCC720 take it as 1 bit transfer,
so if the received character is not 0xFF it is regarded as 0, and if 0xFF is received, it is regarded
as 1. So, to receive 32bit value, a host must transmit 32 bytes with MSB first order.
Figure 14.1 illustrates the transmission of one 32bit value.
Host Transmit Data
= 0xABCD1234
TX (Host)
RX
FF 00 FF 00 FF 00 FF FF
........ ^{00 00 FF FF 00 FF 00 00}
Regarded
as
.... _{1 0 1 0 1 0 1 1}
0 011 0 100
0xA
0xB
Host Transmit Data
= 0xABCD1234
0x3
0x4
Received Data
is packed to
0xABCD1234
Figure 14.1 The waveform of UART transmission
Because of TCC720 always regard none 0xFF data as ‘0’, it is more robust to set the baud rate
of a host UART faster than that of TCC720. The baud rate of a host UART must be as fast as
that the duration of the start bit is shorter than that of TCC720 and longer than the period of
UART clock (XIN/8 or XTIN). But between each transfer cycles, it is recommended to make
sufficient delay times for TCC720 to receive each data correctly.
The procedure of boot code transmission is like as follows. Remember each bit is transferred by
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