ECET $1110-$ Digital Systems I

$16.$ The output pulse width from a $74121$ OS is given by the approximate formula

$t_P$~~$0\mathrm{.}7R_T{C}_T$

Where $R_T$ is the resistance connected between the $\frac{R_{\text{E}\text{x}\text{T}}}{C_{\text{E}\text{x}\text{T}}}$ pin and $V_{CC},$ and $C_T$ is the capacitance connected between the $C_{\text{E}\text{x}\text{T}}$ pin and the $\frac{R_{\text{E}\text{x}\text{T}}}{C_{\text{E}\text{x}\text{T}}}$ pin. The value for $R_T$ can be varied between $2$ and $40k,$ and $C_T$ can be as large as $1000F.$

a$.$ Show how a $74121$ can be connected to produce a negative$-$going pulse with a $5-$ms duration whenever either of two logic signals or $F)$ makes a NGT$.$ Both $E$ and $F$ are normally in the HIGH state.

b$.$ Modify the circuit so that a control input signal, $G,$ can disable the OS output pulse regardless of what occurs at $E$ or $F.$