library(deSolve)
times <- seq(0, 10, by = 1)
signal <- data.frame(times = times, import = rep(0, length(times)))

Text=read.csv("input.csv")

head(signal)
signal$import <- ifelse((trunc(signal$times) %% 2 == 0), 0, 1)
#signal[8:12,]

head(signal)

input <- approxfun(Text, rule = 2)
#input(seq(from = 0.98, to = 1.01, by = 0.005))

SPCmod <- function(t, x, parms) {
  with(as.list(c(parms, x)), {
    import <- input(t)   # <---- here
    dS <- 2*import - b * S * P + g * C
    dP <- c * S * P - d * C * P
    dC <- e * P * C - f * C
    res <- c(dS, dP, dC)
    list(res, signal = import)
  })
}
parms <- c(b = 0.1, c = 0.1, d = 0.1, e = 0.1, f = 0.1, g = 0)
xstart <- c(S = 1, P = 1, C = 1)

out <- ode(y = xstart, times = times, func = SPCmod, parms)
head(out)