1/27/15
SigC667x / SigC641x User Guide, Rev B7
Copyright
Signalogic 2012-2014
107 / 109
6.1 MCBSP Test Mode
In MCBSP test modes, the McBSPs are initialized to transmit and receive 8-bit words at a
frequency of 1 MHz. The last step in initialization for the MCBSP test modes is syncing between
group A and group B DSPs. Because of the fact that the McBSPs come out of reset at different
times due to differences in initialization code and the sync signals are internally generated, group
A and group B DSPs rarely send and receive at the same time initially. This results in the data
received by the group B DSP being a shifted version of the data sent by the group A DSP. In
order to resolve this problem, the group A DSP transmit needs to be synchronized with the group
B DSP receive.
Sync takes place after McBSP1 is initialized on both DSPs. The group A DSP sends a sync
character that cannot be duplicated through a shift of less than 8 bits (we use 0x3c as this
character) for 1 ms. When the group B DSP receives a data word, it checks if the word matches
the sync character. If the sync character was not received, McBSP1 is placed in reset for about an
eighth of a bit period then re-enabled to check for another sync character. This continues until
the expected sync character is received upon which the McBSP1 receive interrupt is enabled.
6.2 UART Test Mode
In UART modes, the McBSPs are initialized to transmit and receive 16-bit words with group A
transmitting at 16 MHz and group B receiving at 1 MHz. Group A expands each bit sent to 16
bits in order for group B to receive each bit once due to the different frequencies. In this way, the
word to be sent is oversampled by a factor of 16 before being sent so that group B receives the
correct word that group A was intended to send.
