SLAZ279AA October   2012  – May 2021 MSP430F5418

 

  1.   1
  2.   2
  3.   3
  4.   4
  5.   5
    1.     6
    2.     7
      1.      8
    3.     9
  6.   10
    1.     11
    2.     12
    3.     13
    4.     14
    5.     15
    6.     16
    7.     17
    8.     18
    9.     19
    10.     20
    11.     21
    12.     22
    13.     23
    14.     24
    15.     25
    16.     26
    17.     27
    18.     28
    19.     29
    20.     30
    21.     31
    22.     32
    23.     33
    24.     34
    25.     35
    26.     36
    27.     37
    28.     38
    29.     39
    30.     40
    31.     41
    32.     42
    33.     43
    34.     44
    35.     45
    36.     46
    37.     47
    38.     48
    39.     49
    40.     50
    41.     51
    42.     52
    43.     53
    44.     54
    45.     55
    46.     56
    47.     57
    48.     58
    49.     59
    50.     60
    51.     61
    52.     62
    53.     63
    54.     64
    55.     65
    56.     66
    57.     67
    58.     68
    59.     69
    60.     70
    61.     71
    62.     72
    63.     73
    64.     74
    65.     75
    66.     76
    67.     77
    68.     78
    69.     79
    70.     80
    71.     81
    72.     82
    73.     83
    74.     84
    75.     85
    76.     86
    77.     87
    78.     88
    79.     89
    80.     90
    81.     91
    82.     92
    83.     93
    84.     94
    85.     95
    86.     96
    87.     97
    88.     98
    89.     99
    90.     100
    91.     101
    92.     102
    93.     103
    94.     104
    95.     105
    96.     106
    97.     107
    98.     108
    99.     109
    100.     110
    101.     111
    102.     112
    103.     113
    104.     114
    105.     115
    106.     116
    107.     117
    108.     118
    109.     119
    110.     120
    111.     121
    112.     122
    113.     123
    114.     124
    115.     125
    116.     126
    117.     127
    118.     128
  7.   129

6.114 USCI34

USCI Module

Category

Functional

Function

I2C multi-master transmit may lose first few bytes.

Description

In an I2C multi-master system (UCMM =1), under the following conditions:

(1)the master is configured as a transmitter (UCTR =1)

AND

(2)the start bit is set (UCTXSTT =1);

if the I2C bus is unavailable, then the USCI module enters an idle state where it waits and checks for bus release. While in the idle state it is possible that the USCI master updates its TXIFG based on clock line activity due to other master/slave communication on the bus. The data byte(s) loaded in TXBUF while in idle state are lost and transmit pointers initialized by the user in the transmit ISR are updated incorrectly.

Workaround

Verify that the START condition has been sent (UCTXSTT =0) before loading TXBUF with data.

Example:
#pragma vector = USCIAB0TX_VECTOR
__interrupt void USCIAB0TX_ISR(void)
{
// Workaround for USCI34
    if(UCB0CTL1&UCTXSTT)
    {
                                                                       // TXData = pointer to the transmit buffer start
                                                                       // PTxData = pointer to transmit in the ISR
        PTxData = TXData;                                   // restore the transmit buffer pointer if the Start bit is set
    }
//
    if(IFG2&UCB0TXIFG)
    {
        if (PTxData < = PTxDataEnd)                      // Check TX byte counter
        {
            UCB0TXBUF = *PTxData++;                 // Load TX buffer
        }
        else
        {
            UCB0CTL1 |= UCTXSTP;                        // I2C stop condition
            IFG2 &= ~UCB0TXIFG;                          // Clear USCI_B0 TX int flag
            __bic_SR_register_on_exit(CPUOFF);      // Exit LPM0
        }
    }
}