We present a new methodology for the construction of high-rate channel modulation run-length-limited RLL codes. Simple modulation encoders and decoders are constructed, with low error propagation during decoding. They combine partial error detection capability (PED) to boost the performance of a concatenated outer Error Correction Code (ECC) [1]. Moreover, current systems are using low redundancy ECC, and the overall rate is mainly determined by the inner modulation code rate, which critically is to be maintained high. Code rates , for example, 16/17, 24/25 and higher are achievable, with efficiency exceeding 0.94 and 0.96, respectively. The proposed fixed length block decodable codes, are generalized schemes of the type for .