MK50H25PLCC datasheet(31/64 Pages) STMICROELECTRONICS

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4.2.4 Timer/Counters

There are 5 independent counter-timers. The Host will write the value of these to the Initialization Block.

COUNTER

DESCRIPTION

MAXIMUM FRAME LENGTH. This field must contain the t wo’s complement of one

less than the maximum allowable frame length, in bytes. Any frame that exceeds this

count will be discarded.

MAXIMUM RETRANSMISSION COUNT. This field must contain the two’s complement

of one less than the maximum number of retransmissions that will be made following

the expiration of T1. If CSR2<14> bit EIBEN=1 then the MK50H25 will expect the value

for counter N2 to be located in the upper byte of IADR + 40.

SCALER

TIMER PRESCALER. Timers T1, T3, and TP are scaled by this number. The prescaler is

incremented once every 32 system clock pulses. When it reaches the timers are incre-

mented and the prescaler is reset. This field is interpreted as two’s complement of the

prescaler period. If CSR2<14> bit EIBEN=1 then the MK50H25 will use the entire 16-bit

value at IADR+08 as the prescaler value. This may be required to achieve long timer

values when operating a high SYSCLK speeds. Note: a prescale value of 1 gives the

smallest amount of scalling to the timers (64 clock pulses); zero gives the largest (8224

clock pulses if EIBEN=0, or 2,097,184 clock pulses if EIBEN=1).

RETRANSMISSION TIMER. Link control frames will be retransmitted upon expiration of

the T1 timer if the appropriate response is not received. This field must contain the two’s

complement of the period of timer T1. The scaled value of T1 should be made large

enough to allow the remote station to receive the control frame and send its response.

T3/T203

LINK IDLE TIMER. The link idle timer determines the amount of link idle time necessary

to consider the link disconnected. If CSR2<12> bit T203E=1 it determines the amount of

link idle time or time without receiving a valid frame before it begins a RR/P=1 polling se-

quence to determine if the link is still connected. This field must contain the two’s com-

plement of the period of T3 or T203. T3 is disabled if CSR5<04> RTSEN = 1 or if the

MK50H25 is in Transparent mode.

IADR + 06

IADR + 08

IADR + 10

IADR + 12

COUNTER N1

TIMER T1

TIMER T3

IADR + 14

TIMER TP

SCALER

COUNTER N2

MK50H25

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